Implement first iteration of node

The coordinator implementation has been refactored to allow all the goroutines
to be handled from the node.

common/accountcreationauths.go

@@ -12,5 +12,5 @@ type AccountCreationAuth struct {
 	Timestamp time.Time
 	EthAddr   ethCommon.Address
 	BJJ       babyjub.PublicKey
-	Signature babyjub.Signature
+	Signature []byte
 }