Ruthie's Ajax scheduling upgrades

This is the partial result of Ruthie's long-term project to improve Ajax scheduling:
- Added a more flexible 2-column UI
- Added a change log
- Added several types of filters for class directory
- Added both backend and frontend (Selenium) tests

This should be tested, reviewed and merged in the next week.  Hopefully this will be easy since the code looks fairly mature.

I'll let Ruthie comment more as she sees fit.