Import & adapt iden/go-iden3-core/eth/client

Add PoolL2Tx verify signature needed methods

Implements the hash to be signed from PoolL2Tx, compatible with javascript version.
Implements the signature verification for a given PoolL2Tx.

Add TxCompressedData & V2 with some extra parsers for common

Unify StateDB MT{Create/Update}Account

Previously as the txprocessor.go methods were specific for the BatchBuilder,
the MTCreateAccount & CreateAccount and MTUpdateAccount & UpdateAccount were
also designed to be used by BatchBuilder and TxSelector depending on the
MerkleTree usage calling one kind of method or anotherone.

But now that this methods are being called directly by the StateDB (through the
methods in txprocessors.go), to allow also the methods usage from the
Synchronizer, there can not be the MT and no-MT methods separated, so this
commit unifies MTCreateAccount with CreateAccount, and MTUpdateAccount with
UpdateAccount, which internally will update the MerkleTree depending if the
specific StateDB in usage has the MerkleTree defined or not.

Feature/testing framework language

Migrate TxProcessors from BatchBuilder to StateDB in order to be used by
BatchBuilder & Synchronizer

Add test-lang Fee & ForceExit option

Add log system

Update SQL schemas

Feature/statedb checkpoints

* 16 bits fix encoding

* Types modification

* Rounding loss check

* Clean up a bit and add benchmarks

Unneded usage of big.Int has been removed

Conversion methods are now methods/constructors of Float16 to make the code
more idiomatic.

Co-authored-by: Toni Ramírez <toni@iden3.com>
Co-authored-by: arnaucube <root@arnaucube.com>
Co-authored-by: Eduard S <eduard@iden3.io>

Initial Coordinator (OpManager) structure

Remove goarch 386 and go-version 1.13 from GHA

Integrate TxSelector with StateDB

Feature/batchbuilder integratedb

Co-authored-by: Eduard S <eduard@iden3.io>

Add StateDB & LocalStateDB

Co-authored-by: Eduard S. <eduard@iden3.io>

Feature/batchbuilder init

Co-authored-by: Eduard S. <eduard@iden3.io>

Add common/Leaf struct & parsers (bigint & byte arrays)

Update to follow DB spec

* First price-updater implementation

* Lint corrections

* Structs revision

* Read Write Mutex

* Review price updater and apply small changes

Co-authored-by: Toni Ramírez <toni@iden3.com>
Co-authored-by: Eduard S <eduard@iden3.io>

Definition of txpool interface

Initial draft of the common structs