- KVDB/StateDB
        - Pass config parameters in a Config type instead of using many
          arguments in constructor.
	- Add new parameter `NoLast` which disables having an opened DB with a
	  checkpoint to the last batchNum for thread-safe reads.  Last will be
	  disabled in the StateDB used by the TxSelector and BatchBuilder.
	- Add new parameter `NoGapsCheck` which skips checking gaps in the list
	  of checkpoints and returning errors if there are gaps.  Gaps check
	  will be disabled in the StateDB used by the TxSelector and
	  BatchBuilder, because we expect to have gaps when there are multiple
	  coordinators forging (slots not forged by our coordinator will leave
	  gaps).

PoolL2Tx.Info contains information about the status & State of the
transaction. As for example, if the Tx has not been selected in the last
batch due not enough Balance at the Sender account, this reason would
appear at this parameter.
This will help the client (wallet, batchexplorer, etc) to reason why a
L2Tx is not selected in the forged batches.

- TxSelector
	- Add check enough funds on sender at TxSelector and don't
include the tx in the selection
- TxProcessor
	- Add checks that the balance when substracted the
amount/amount+fee never goes below 0

fix #502

Update account.PublicKey to account.BJJ for naming consistency with the rest of the code

- Upgrade go-merkletree version to include the last changes of Pebble
that fixes the cgo issues (which should fix #453), from:
c2b05f12d7
- TxSelector
	- Remove parameter batchNum for GetL2TxSelection & GetL1L2TxSelection
	- Add checks of ToBJJ & ToEthAddr when ToIdx>255
	- Avoid getting the sender account twice to get the TokenID of a l2tx
	- Add test to check that selected L2Txs are sorted by Nonce
	- Discard L2Tx that return error at ProcessL2Txs
- executed `go mod tidy`

- Add missing Fees to CoordAccounts after processing PoolL2Txs
- Add Nonces checks for L2Txs (txs with incorrect nonces not included
in the selection)
- Add missing MakeCheckpoint() at the LocalAccountsDB once the
selection is done
- Add TxSelector test of full flow using Til.SetBlockchainMinimumFlow0
checking balances & parameters

- StateDB
  - Update GetIdxByEthAddrBJJ to return ErrToIdxNotFound when idx not found, so can be checked at upper levels
- TxSelector
  - rm CoordIdxsDB that is no longer needed (also related methods)
  - add `getCoordIdx` method to get the Coordinator Idx for a given TokenID
  - Update coordinator account creation related to new TokenIDs from L2Txs
  - Reorganize GetL1L2TxSelection
  - return CoordIdxs used in the selection
- Update go-merkletree version which avoids marshaling Siblings to json
with 'null' value in case of empty array

- Abstract TxProcessor from StateDB
- Upgrade to last version of go-merkletree for the key-value DB usage

Introduce a constructor parameter for the StateDB called `keep`, which tells
how many checkpoints to keep.  When doing a new checkpoint, if the number of
existing checkpoints exeeds `keep`, the oldest ones will be deleted.

Add return of AccountCreationAuths at the TxSelector, which is an array
of bytearrays with the signatures of the AccountCreationAuthorization of
the accounts of the users created by the Coordinator with
L1CoordinatorTxs of those accounts that does not exist yet but there is
a transactions to them and the authorization of account creation exists.

- Implement Pipeline.prepareForgeBatchArgs()
- Add a minimal stress test for the coordinator (that also runs the
  synchronizer)
- Update txprocessor.ProcessTxs() to return valid results for batches without
  transactions
  	- Add the boilerplate for the corresponding test, leaving as TODO the
	  zkInput values
- Update prover client to use the same point format as proof server (projective)
- Update interface of TxSelector.GetCoordIdxs to also return the authorizations
  to create accounts that go with the l1CoordinatorTxs.

Update usage of `*babyjub.PublicKey` to `babyjub.PublicKeyComp`
- when the key is not defined, internally is used `babyjub.EmptyBJJComp`, which is a `[32]byte` of zeroes of type `babyjub.PublicKeyComp`
- the API continues returning `nil` when the key is not defined

TxTypeToEthAddr & TxTypeToBJJ

- TxSelector
	- Add SelectionConfig for each batch
	- Add CoordIdxDB key-value where the CoordinatorIdxs are stored
	- Separated method for filtering TxTypeToEthAddr & TxTypeToBJJ

- Common
	- Add `IdxNonce` type used to track nonces in accounts to invalidate
	  l2txs in the pool
- Config
	- Update coordinator config will all the new configuration parameters
	  used in the coordinator
- Coordinator
	- Introduce the `Purger` to track how often to purge and do the job when
	  needed according to a configuration.
	- Implement the methods to invalidate l2txs transactions due to l2txs
	  selection in batches.  For now these functions are not used in favour
	  of the `Purger` methods, which check ALL the l2txs in the pool.
	- Call Invalidation and Purging methods of the purger both when the
	  node is forging (in the pipeline when starting a new batch) and when
	  the node is not forging (in coordinator when being notified about a
	  new synced block)
- L2DB:
	- Implement `GetPendingUniqueFromIdxs` to get all the unique idxs from
	  pending transactions (used to get their nonces and then invalidate
	  txs)
	- Redo `CheckNonces` with a single SQL query and using `common.IdxNonce`
	  instead of `common.Account`
- StateDB:
	- Expose GetIdx to check errors when invalidating pool txs
- Synchronizer:
	- Test forged L1UserTxs processed by TxProcessor
	- Improve checks of Effective values
- TxSelector:
	- Expose the internal LocalStateDB in order to check account nonces in
	  the coordinator when not forging.

Add HashGlobalInputs for ZKInputs compatible with js & circom circuits version.

Compatible with hermeznetwork/commonjs at version: c6a1448db5
(c6a1448db5)

- Add TxSel Nonce sort
- Fix surplus from refactors
- StateDB reuse computation of ToIdx across Synchronizer, TxSelector,
BatchBuilder

- Implement SlicePtrsToSlice and use it in all `meddler.QueryAll` sql db functions to always return []Foo instead of []*Foo

- Implement new TxID spec that distinguishes L1UserTx and L1CoordinatorTx
- Replace some type []*Foo by []Foo
- Fix HistoryDB & L2DB bug: in case of error, a rollback was applied and the returned error was nil
- Reorder inserts in historydb.NewHistoryDB() to follow foreign key dependencies
- Add initial synchronizer test with test.Client (for now, only tested l1UserTxs, blocks, addToken)
- Update L1UserTx event in test.Client

* WIP: rebase

* Make nullable fields use pointers

Add StateDB compute nonces on ProcessTx L2Tx, and update StateDB for
type TypeSynchronizer, TypeTxSelector, TypeBatchBuilder

Add TxID calculation & New{Layer}Tx Type

New{Layer}Tx methods that compute the `TxID` & `TxType` values from the
transaction values:
- NewL1Tx
- NewL2Tx
- NewPoolL2Tx

Add TxID Scanner & Valuer for database/sql

HistoryDB & L2DB & API packages tests will need to be addapted to the
TestTransaction generation once is done.

* WIP rebase

* Combine both SQL DBs

* API and DB refactor

- GetL2TxSelection & GetL1L2TxSelection integrated with dbs
- Create L1CoordinatorTx of type CreateAccountDeposit when a L2
requires it (and the AccountCreationAuth exists)

Update StateDB to new & ExitInfo struct & BatchNum
Also a small fix at txselector & log packages