Favorites

Couple of notes
The following are temporary changes I made while implementing the favorites feature that I reverted back to their original states before making this pull request:

I had to bump the Ruby version to 2.1.1 because rbenv said bundler didn't exist in 2.1.2 o_0
I also had to create a local redis server (or whatever redis thing is in redis.rb)
I also added the Faker gem in development for manual browser testing (I also wrote a basic integration test no worries).

Other notes:
All the tests would throw an error (for me at least) I think due to the migration changing the 'stack' column to 'course' in the codefellows_courses table. I changed the codefellows_courses.yml fixtures that had 'stack' to 'course' so the tests wouldn't throw me an error. I don't know how you guys didn't run into this issue when running tests but whatever.