- Add config parameter `Coordinator.L2DB.MinPriceUSD` which allows rejecting
  txs to the pool that have a fee lower than the minimum.
- In pool tx insertion, checking the number of pending txs atomically with the
  insertion to avoid data races leading to more than MaxTxs pending txs in the
  pool.

- In tx_pool, add a column called `external_delete` that can be set to true
  externally.  Regularly, the coordinator will delete all pending txs with this
  column set to true.  The interval for this action is set via the new config
  parameter `Coordinator.PurgeByExtDelInterval`.
- In tx_pool, add a column for the client ip that sent the transaction.  The
  api fills this value using the ClientIP method from gin.Context, which should
  work even under a reverse-proxy.

Migrate all packages to use Float40 & Add more test vectors at common

- 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).

Last db view is an opened pebble db which always contains a checkpoint from the
last batch.  Methods to access this last batch are thread safe so that views of
the last checkpoint can be made anywhere and with a consistent view of the
state.

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.

- TxProcessor move txCompressedDataEmpty inside the if of tp.zki!=nil
- Abstract generation of transactions for ZKInput tests to avoid code
repetition
  - used at txprocessor & test/zkproof tests

- Add ZKI tests Til last batches MinimumFlow0
- Fix zki.CurrentNumBatch
- Fix StateDB BatchNum log

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

- 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.

- Fix AccountCreationAuth.HashToSign (was using `[]byte("0x...")`, which
uses the bytes of the string. Now uses the bytearray of the compressed
BJJ public key (compatible with js implementation))
- Update AccountCreationAuth to last specification (add to hash
parameters ChainID & HermezAddress)
- Add missing test to AccountCreationAuth

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

- API:
	- Replace `emergencyModeStaringTime` by `emercengyModeStartingBlock`
- Synchronizer:
	- Track emergency mode starting block
- cli/node
	- Add working coordinator config
- coordinator:
	- Retry handler for synchronizer stats in case of error (instead of
	  waiting for the next block to try again)
	- On init, trigger an initial call to the handler for synced block
	  before waiting for the synchronizer, to force the coordinator to start
	  its logic even if there's no new block right after the node has been
	  started (very useful for running in testnet where the frequency of
	  blocks is variable)
	- Merge Msg for synced block and updated vars into one: `MsgSyncBlock`.

- API
	- When updating network info, handle cases where no batches exists and
	  where no forgers exists
- cli/node
	- Update `cfg.buidler.toml` config file to a working version
- common
	- Add new smart contract structs and extend some existing ones to
	  reflect updates regarding events from the smart contracts
- SQL
	- Add new tables and extend existing ones to reflect updates regarding
	  events from the smart contracts
- db/historydb
	- Add functions to insert new smart contract events data
	- Fix unclosed rows that led to inconsistent sql driver state (replace
	  NamedQuery by NamedExec).  This fixes the error:
	  `pq: unexpected Parse response 'C'`
- db/l2db
	- Close rows after usage
- eth
	- In Rollup event, introduce a new UpdateBucketsParameter when there's a
	  SafeMode event, with `SafeMode = true`
- synchronizer
	- synchronize new events
	- avoid calling `auction.CanForge` before the genesisBlock to avoid
	  getting a revert.

Related to 445f26ec9f