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

- 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

- 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

- 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

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

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