Save Logs to DB (#100)

* Save logs to database

* Save multiple logs to db

* Add block number parameter to `FindLogs`

pkg/core/log.go

@@ -4,6 +4,7 @@ type Log struct {
 	BlockNumber int64
 	TxHash      string
 	Address     string
-	Topics      []string
+	Topics      map[int]string
+	Index       int64
 	Data        string
 }