Add TxSel Nonce sort. Fix surplus from refactors

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

Impl exit edpoint and refactor pagination

Feature/transakcio

Add transakcio set type definition, add set loading, move transakcio to
package, adapt branch to last master updates (fix compile due new common
types & git conflicts).
Update tests to pass the test, pending to adapt to new Transakcio
interface.

Fix PR #187

(#187 PR was done before another PR (#186) was merged into master, and
when 187 was merged to master, was not compiling due changes from #186
not applied yet to #187)

Update ethclient rollup iteration 2

Change pointers to nil in common (remove common.Struct.parameters pointers for Idx & EthAddr.  Update common parameters)

Feature/integration2

- 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

Update ethclient contracts & rollup iteration 1

Add methods to get ERC20 constants

Add L1CoordTx & L2Tx byte parsers functions

* WIP: rebase

* Make nullable fields use pointers

Connect price updater to historydb

Add StateDB compute nonces on ProcessTx L2Tx

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

Have BigInt be a proper big value that has 18 decimals

Update test ethclient and coordinator

Update TxProcessor L2Tx logic for case ToIdx==0

Add TxID calculation & New{Layer}Tx Type

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.

Update ethclient contracts & add wdelayer events

* WIP rebase

* Combine both SQL DBs

* API and DB refactor

Update ethclient wdelayer & add auction events

Helper methods for Synchronizer and TX refactor

Idx to 6 bytes (48 bits)