Renamed ServiceHelper to ServiceExecutor 

1. Renamed ServiceHelper to ServiceExecutor and updated class description accordingly
2. Renamed private members “serviceHelper” to “serviceExecutor “ in all Service classes.
3. Introduced new ServiceHelper class to support common auxiliary operations required across multiple services.  Updated getByCustomView() methods to use method from ServiceHelper class.

4. Miscellaneous: removed a few no longer used Strings from ApiData.java