Feature/cdap 868 app fabric http handler refactor

First stab at refactoring ``AppFabricHttpHandler``. Moved all ``application`` level actions to class ``AppHelper`` and all ``program`` level actions to class ``ProgramHelper``.

Currently tested on standalone mode. Brought up CDAP, loaded multiple apps.  started services/flows. ran queries. No errors encountered. 

https://builds.cask.co/browse/CDAP-DUT290 passed.
Sure, I did not change any logic in this PR. Just did refactor. But this could be good time to remove it.