Add receipts (#119)

* Conversion between Geth Receipt and core.Receipt

* Add receipt to DB

* Insert receipts with transactions

* Update Travis CI to use dep for dependencies

pkg/core/transaction.go

@@ -8,5 +8,6 @@ type Transaction struct {
 	From     string
 	GasLimit int64
 	GasPrice int64
-	Value    int64
+	Receipt
+	Value int64
 }