Legacy URL support

Pivotal Tracker: https://www.pivotaltracker.com/story/show/65353110
* added ``friendly_id`` gem for prettified urls
* added special case in route for legacy urls
* updated ``projects`` and ``documents`` templates
* added rake task to ``db:regenerate_slugs`` to generate slugs for slug-less models
* updated cucumber and rspec tests to accomodate changes