[CDAP-1060] Implemented v3 workflow/schedule apis

Added v3 schedule endpoints.

Note: The schedule APIs still do not use ``namespaceId``. This PR just ensures that ``namespaceId`` is available. It needs to be applied while performing schedule actions. That will come in a future PR.

This PR ensures parity with v2 APIs, which weren't using ``accountId`` for schedules.
Fixed. The ``/current`` endpoint is broken right now (https://issues.cask.co/browse/CDAP-66) which the reason why I couldn't test this completely so it didn't get caught. Have added a test in ``ProgramLifecycleHttpHandler`` for the ``/current`` endpoint which should be enabled after CDAP-66 is fixed.