Add max txs limit to tx pool

Sanitize varchars that may not be UTF-8

Feature/txselector0

- 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

- Til
  - tests that were using `til.SetBlockchainMinimumFlow0` have been
updated, as now the L1CoordinatorTxs are placed simulating TxSelector
creation (when needed, not before)
  - Add `EthSk` to `tc.User` to allow to sign `AccoutCreationAuths` at
the tests flows
- TxProcessor
  - for L2Txs get TokenID from tx.FromIdx Account.TokenID instead than
  - update tests vectors for new values
from tx.TokenID (which not always is set)
- Common
  - move TxIDsFromL2Txs & TxIDsFromPoolL2Txs from `coordinator` to
`common` to allow usage from other packages

Change queries that produced undesired meddler logs

Add config flag to enable/disable meddler logs

Added new metrics tests

Update TxSelector to return CoordIdxs used & other

- 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

- In config, add Debug.MeddlerLogs to enable meddler debug logs.  This only
  affects the node started via cli, tests swill ran with `meddler.Debug = true`
- Remove unused ethereum client functions and config parameters
- Document all the config parameters

Add circuit configuration to node config

- Remove MaxL1CoordTxs parameter from the TxSelector because this parameter
  doesn't exist
- Use ChainID in l1tx byte encoding
- Pass txprocessor configuration to batch builder via an existing parameter

Add cli command to wipe the SQL DB

- Refactor the migrations code so that packr is only called (via an init
  function in `db/utils.go`).
- When loading the migrations, make sure there is at least one migration,
  otherwise panic (this would happen if the node is built incorrectly)

Load ethereum private key

empty array instead of 404

Update ExitProofs-Siblings padding

Load an ethereum keystore when the node is started in coordinator mode.  The
private key corresponding to the forger address must be imported into the
keystore before running the node in coordinator mode.  You can see an examples
in `cli/node/load-sk-example.sh`.

Include addrs in exit responses

Fix next forgers when no bids

Abstract KVDB from StateDB

- KVDB contains the Checkpoint & Resets system
- StateDB uses KVDB and adds all the StateDB related methods

Fix next forgers api response

Fix item_id order in forged l1UserTxs

Also, make sure that all SQL queries that return slices are sorted

Abstract TxProcessor from StateDB

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

Fix ZKI NTx for MaxTx

AccountCreationAuth compatible with js implementation

On the Circuits uses the name `nTx` (and on the tests `maxTx`), but
Contracts `maxTx`. On Go we had both variables, but really only used
one, now at Go we use `MaxTx` to refer to the maximum number of
transactions.

Delete old checkpoints in stateDB automatically & Don't log errors when context done

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.

TxSel return of AccCreatAuths from the selection

Update AccountCreationAuth & fix auth.HashToSign

- 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

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.

Sync ForgerCommitment and use it in coord