Split locations controller into separate public/private controllers

Currently `LocationsController.php` has the public and admin specific methods in the one controller. This combination of two different security access levels [causes a weird and dangerous if statement in secured controller](https://github.com/NUBIC/halon/blob/master/app/controllers/SecuredController.php#L22). This controller should be split up into a public controllers an admin controller that inherit from an abstract base controller which contains the index method.