Added basic Sidebar, /api/v0 namespacing, user_groups table

I added basic Sidebar functionality, put the server within an API/V0 namespacing, and added the user_groups database. 

I created a users_controller file and by default the first user (after you've seeded it) will be the one that is considered 'logged in' for purposes of the data that is being retrieved. 

The sidebar currently has a "subscribed" and a "popular" groups lists. The subscribed one will return the groups that the current user is subscribed to. It pulls that in via AJAX and then again everytime you click on it the sidebar it will make another ajax request.