feat: add ContractResult.Status

add ContractResult.Status.Executing to represent that the contract request has been added into blocks and waits for execution

src/main/base/org/bdware/sc/ContractResult.java

@@ -26,6 +26,6 @@ public class ContractResult {
     }
 
     public enum Status {
-        Success, Exception, Error
+        Success, Exception, Error, Executing
     }
 }