Creates shifts for bars and associated actions and associations

* Edit, update, destroy limited to bar_owner
* Creates partials for shift views
* Shifts are created by the bar owner and will be filled/taken by bartenders
You are correct in how the controller functions, but the controller won't *validate* the data to be that way. You might consider adding a validation that *requires* that every Shift is associated with a Bar. That way you can be sure that no bad data ever enters the system. 

Let me know if that makes sense.