Feed integration with CIT website

Added a courses#cit_feed action to support integration with the main CIT
website (currently managed with Expression Engine (EE)).  We'll expose
several feed formats, and then we can see which format works best with
EE.

Exposed feed formats/endpoints are

- [x] List of all available courses
  - [x] JSON
  - [x] RSS
  - [x] Atom
  - [x] CSV
- [x] List of top N upcoming courses/sections
  - [x] JSON
  - [x] RSS
  - [x] Atom
  - [x] CSV

That should give us a good variety to choose from...I hope.  We can always add more later if we need.