Advance coordinator implementation

- Common
	- Move ErrTODO and ErrDone to common for usage where needed.
- Coordinator
	- Move prover types to prover package
	- Handle reorgs, stopping the pipeline when necessary
	- Handle ethereum transaction errors by stopping the pipeline
	- In case of ethereum transaction revert, check for known revert causes
	  (more revert causes can be added to handle more cases)
	- Fix skipped transactions in TxManager confirmation logic
	- Cancel and wait for provers to be ready
	- Connect L2DB to:
		- purge l2txs due to timeout
		- mark l2txs at the different states
	- Connect HistoryDB to query L1UserTxs to forge in an L1Batch
- L2DB
	- Skip update functions when the input slices have no values (to avoid a
	  query with no values that results in an SQL error)
- StateDB
	- In LocalStateDB, fix Reset when mt == nil
- Prover (new package)
	- Rename the interface to Prover
	- Rename the mock struct to Mock
	- Extend Prover interface methods to provide everything required by the
	  coordinator
	- Begin implementing required http client code to interact with server
	  proof (not tested)
- Synchronizer:
	- Add LastForgeL1TxsNum to Stats
- Test/Client
	- Update Auction logic to track slots in which there's no forge during
	  the time before the deadline (following the solidity implementation)

db/statedb/statedb.go

@@ -541,7 +541,8 @@ func (l *LocalStateDB) Reset(batchNum common.BatchNum, fromSynchronizer bool) er
 		// use checkpoint from SynchronizerStateDB
 		if _, err := os.Stat(synchronizerCheckpointPath); os.IsNotExist(err) {
 			// if synchronizerStateDB does not have checkpoint at batchNum, return err
-			return tracerr.Wrap(fmt.Errorf("Checkpoint not exist in Synchronizer"))
+			return tracerr.Wrap(fmt.Errorf("Checkpoint \"%v\" not exist in Synchronizer",
+				synchronizerCheckpointPath))
 		}
 
 		if err := l.db.Pebble().Close(); err != nil {
@@ -576,11 +577,13 @@ func (l *LocalStateDB) Reset(batchNum common.BatchNum, fromSynchronizer bool) er
 			return tracerr.Wrap(err)
 		}
 		// open the MT for the current s.db
-		mt, err := merkletree.NewMerkleTree(l.db.WithPrefix(PrefixKeyMT), l.mt.MaxLevels())
-		if err != nil {
-			return tracerr.Wrap(err)
+		if l.mt != nil {
+			mt, err := merkletree.NewMerkleTree(l.db.WithPrefix(PrefixKeyMT), l.mt.MaxLevels())
+			if err != nil {
+				return tracerr.Wrap(err)
+			}
+			l.mt = mt
 		}
-		l.mt = mt
 
 		return nil
 	}