Replace add course lightbox with browse-like page

[sethwoodworth]

This is mutually exclusive with #205. We need to decide between them.

Instead of having an autocomplete lightbox, what if we have a full "add courses" page that does the following:

• on page load, it displays a list of courses from your school in a list
• The list would need to have a denser display than the current courses list
• there would be a search box at the top of the page that would hide all courses in the list that do not match the search
  • this can be done in javascript on the client side
• each course would have add or drop button based on enrollment status