fixes #812 - new permissions model, user group role and nest support, role filters for better granularity

• Daniel Lobato <elobatocs@gmail.com>
• Joseph Magen <jmagen@redhat.com>
• Tom McKay <thomasmckay@redhat.com>
• Greg Sutcliffe <gsutclif@redhat.com>...

Fixes #170 - implement usergroups

Added migration
Added tests
Added MVC files
Added the routes as well
Added the program logic and additional views
Added RESTful actions for update and create
Added validations to ensure that usergroup.name and user.login do not collide...