#355, #356, #357 Refactoring Issues

#355: `application_setup_controller` and `users_controller` had duplicated methods to set new users. Outsourced into a module and loaded into each controller.

#356: `set_view_mode` in `application_controller` was too redundant. Removed redundant if/else statements.

#357: Removed dead code from activate and deactivate methods in `application_controller` and separated `require_admin` logic into `before_filter`.