TABDEV-3384: Ensure JivePost objects include their status in the toJSON method. Refactor JiveContentTests to allow a different set of assertions in subclass tests.

This is required to ensure drafts can be created by setting the status to incomplete.
Merge branch 'feature/TABDEV-3384' into develop

* feature/TABDEV-3384:
  TABDEV-3384: Ensure JivePost objects include their status in the toJSON method. Refactor JiveContentTests to allow a different set of assertions in subclass tests.