Refactored Posts API v2 controller
Refactored Posts API v2 controller

refs https://github.com/TryGhost/Team/issues/949

- This refactor is needed to bring the code in line with the rest of post API controllers
- Next step will extract shared code patterns into a separate module

e10/Ghost,ErisDS/Ghost,TryGhost/Ghost,janvt/Ghost,ErisDS/Ghost,TryGhost/Ghost,TryGhost/Ghost,janvt/Ghost,e10/Ghost,ErisDS/Ghost