Move WatchedContract back to core

pkg/core/blockchain.go

@@ -8,5 +8,6 @@ type Blockchain interface {
 	StartListening()
 	StopListening()
 	GetContract(contractHash string) (Contract, error)
+	GetContractAttributes(contractHash string) (ContractAttributes, error)
 	GetAttribute(contract Contract, attributeName string, blockNumber *big.Int) (interface{}, error)
 }

pkg/core/watched_contract.go

@@ -0,0 +1,7 @@
+package core
+
+type WatchedContract struct {
+	Abi          string
+	Hash         string
+	Transactions []Transaction
+}