Fix API nonces

Update packr to 2.8.1 which fixes this issue:
https://github.com/gobuffalo/packr/issues/261 which I encountered while running
a test with `-race`

- Implement Pipeline.prepareForgeBatchArgs()
- Add a minimal stress test for the coordinator (that also runs the
  synchronizer)
- Update txprocessor.ProcessTxs() to return valid results for batches without
  transactions
  	- Add the boilerplate for the corresponding test, leaving as TODO the
	  zkInput values
- Update prover client to use the same point format as proof server (projective)
- Update interface of TxSelector.GetCoordIdxs to also return the authorizations
  to create accounts that go with the l1CoordinatorTxs.

Test purger, fix some nonces

- Test all the purger functions
- Fix nonces set by til (previously til started with nonce 1 for pool l2txs,
  but the correct implementation is to start with nonce 0)
- Rename L2DB.CheckNonces to L2DB.invalidateOldNoncesQuery
- Rename L2DB.checkNoncesQuery to L2DB.InvalidateOldNonces

Related https://github.com/hermeznetwork/hermez-node/issues/392 (Fix checkNoncesQuery)
Resolve https://github.com/hermeznetwork/hermez-node/issues/396

Feature/bjj comp

Update usage of `*babyjub.PublicKey` to `babyjub.PublicKeyComp`
- when the key is not defined, internally is used `babyjub.EmptyBJJComp`, which is a `[32]byte` of zeroes of type `babyjub.PublicKeyComp`
- the API continues returning `nil` when the key is not defined

Update and integrate price updater

Use init SC vars and start block from events

Fix historyDB GetBestBidCoordinator

PriceUpdater:
    - Pass context so that it can be canceled during an update loop
    - Define APITypes to make it explicit which API we are using

Previously the Synchronizer required the initial variables of the smart
contracts to be passed as a configuration parameter (that the node took from
the configuration file).  The same applied to the blockNumber.

The last update of the smart contracts introduced events for each smart
contract constructor (initializer), which allows querying the initial variables
as well as the initial block number for each smart contract.

Now the synchronizer uses this information, and thus the initial variables and
the starting block numbers have been removed from the configuration.

Upgrade contracts and parse init events

Effective amounts add missing check

TxSelector add CoordIdxDB, SelectionConfig, abstract filtering

TxTypeToEthAddr & TxTypeToBJJ

- TxSelector
	- Add SelectionConfig for each batch
	- Add CoordIdxDB key-value where the CoordinatorIdxs are stored
	- Separated method for filtering TxTypeToEthAddr & TxTypeToBJJ

Fix order of L1UserTxs

When the synchronizer queries the unforged L1UserTxs, sort them by position

Swap the order of calls setL1UserTxEffectiveAmounts and addBatch in
AddBlockSCData because otherwise, for reasons I dont understand, the item_id of
the txs doesn't follow the position of the txs.

Fix panic caused by nil batchInfo.ServerProof

Fix coordinator pipeline forgeBatch call

Merge node (sync-only) and coord config

Make coordinator more robust agains failed forges

Fix format of the MTP for exit endpoint

Update txs constructors and helpers

Add mock proof server

Extend Coordinator tests

For each tx, move the logic of setting the Type and TxID to separate functions,
so that they can be called when necessary.

In synchronizer, set all the required fields using the `SetID` and `SetType`
for l2txs when needed.  This is necessary because the `ProcessTxs()` works with
`common.PoolL2Tx`, which misses some fields from `common.L2Tx`, and because
`ProcessTxs()` needs the Type to be set, but at the same time `ProcessTxs()`
sets the Nonce, which is required for the `TxID`.

Fix inconsistency between api doc and code: hermezEthereumAddress => …

Update StateDB computeEffectiveAmounts

Add TxType before processing L2 tx

For the case of tx.EthAddr!=tx.FromIdx.EthAddr

Fix queries when no rows

Update ZKInputs generation:

Make coordinator more responsive