Creates shifts for bars and associated actions and associations

* Edit, update, destroy limited to bar_owner
* Creates partials for shift views
* Implements before_action filter for shift edit, update, destroy actions
* Implements before_action filter (logged_in) in layouts/application
* Adds validations and db contraints to shifts
Merge pull request #11 from mtdowd/schedule

Creates shifts for bars and associated actions and associations