Signing in brings you to your dashboard instead of the courses page with a find courses button when not enrolled.

redesigns course item on home page and find courses page, refactors its implimentation and makes vrious other design improvements

These are then displayed at /courses.

* use clearer names for the two status strings passed to js
* add functions to do canonical conversion of progress to js string
* fix updating bug in sequence.coffee
* add some todo comments and other docs to make future expansion easier

* change bottom border of links:
  red for not started
  yellow for in_progress
  green for done

* This should probably be designed at some point.
* Obvious problems: the yellow is not very visible, and lots of people are
  red/green color-blind.