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 technically finding `@shift` twice.. Once in the `require_owner` and again in the actual controller action. Maybe you can also run `find_shift` in a `before_action` filter before the `require_owner` so that it only has to be found once. 

Let me know if that makes sense. 

Great job!