Dependencies Update

Pivotal Tracker: https://www.pivotaltracker.com/story/show/79647948

* Updating Ruby to 2.1.3 and Rails to 4.1.6 and other dependencies to their latest versions.
* Locking `sass-rails` and `jquery-turbolinks` because they newer versions were buggy.

Fixes #474
Devise doesn't accept strings as resource_name anymore.