Improve stateDB reliability

- Close StateDB when stopping the node
- Lock the StateDB when doing checkpoints to avoid multiple instances of
  oppening the pebble DB at the same time.

Update TxID to use eth Keccak256

Fix api resopnse format for recommended fee

- Update TxID to use eth Keccak256
- Added more tests to L2Tx TxID calculation to check compatibility with
js version from https://github.com/hermeznetwork/hermezjs/pull/57

Update README

Use Warn instead of Error on get prices error

Update contracts and get verifiersLen from SC

Fix incorrect initial CurrentIdx in kvdb

Check enough funds on sender at TxSelector and don't include the tx in the selection

- TxSelector
	- Add check enough funds on sender at TxSelector and don't
include the tx in the selection
- TxProcessor
	- Add checks that the balance when substracted the
amount/amount+fee never goes below 0

fix #502

Feature/txid fixcollisions

L2Tx.TokenID is not on the data obtained by the Synchronizer from the
blockchain, but is set by the TxProcessor when processing the
transactions in the StateDB.

run integration on push to master

Fix exit tree nonces

Remove increment in exit tree leaf nonce when there are multiple exits for the
same account in the same batch.

Add a test to verify the correct implementation of exit leafs caused by
multiple exits.

Update coordinator to work better under real net

- cli / node
    - Update handler of SIGINT so that after 3 SIGINTs, the process terminates
      unconditionally
- coordinator
    - Store stats without pointer
    - In all functions that send a variable via channel, check for context done
      to avoid deadlock (due to no process reading from the channel, which has
      no queue) when the node is stopped.
    - Abstract `canForge` so that it can be used outside of the `Coordinator`
    - In `canForge` check the blockNumber in current and next slot.
    - Update tests due to smart contract changes in slot handling, and minimum
      bid defaults
    - TxManager
        - Add consts, vars and stats to allow evaluating `canForge`
        - Add `canForge` method (not used yet)
        - Store batch and nonces status (last success and last pending)
        - Track nonces internally instead of relying on the ethereum node (this
          is required to work with ganache when there are pending txs)
        - Handle the (common) case of the receipt not being found after the tx
          is sent.
        - Don't start the main loop until we get an initial messae fo the stats
          and vars (so that in the loop the stats and vars are set to
          synchronizer values)
- eth / ethereum client
    - Add necessary methods to create the auth object for transactions manually
      so that we can set the nonce, gas price, gas limit, etc manually
    - Update `RollupForgeBatch` to take an auth object as input (so that the
      coordinator can set parameters manually)
- synchronizer
    - In stats, add `NextSlot`

Feature/fixexitinfos

Fix #497

The smart contracts were updated at some point and there have been some changes
in slot calculation.  Update these values in the synchronizer and test auction
smart contract implementaiton.

- Test that two exits for the same account in the same batch should be merged
  into one exitInfo with the accumulated balance of both exits, in the
  txprocessor output

Fix CoordIdxs fees duplicated

Fix #483

Stop using hardcoded bootcoordinator in api

Add test connecting TxSelector, BatchBuilder, ZKInputs, ProofServer

- Add tests connecting TxSelector, BatchBuilder, ZKInputs, ProofServer
- Added test to check that the signatures of the PoolL2Txs from the L2DB
pool can be verified, to check that the parameters of the PoolL2Tx match
the original parameters signed before inserting them into the L2DB

In pool l2tx, store effective in aux column

Add ZKInputs test to use ProofServer

Add idx for txs that create account

Document that /tmp should be mounted as tmpfs

Fix ChainID in zkInputs empty TxCmpData

- 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

Resolve #214

Test TxProcessor zkInputs against a real proof server

Add opt to disable print logs but storing to file