I apologize for the state of this change--there's no good way to break it up.
This change does a bunch of things:

- Add a (very WIP) admin page.

- Use express-restify-mongoose to make a REST API to do CRUD on our mongoose

  schemas. This is enhanced a bit with some access control.

- Add a new group model.

- Refactor the front page to use the new APIs where possible. This obsoletes

  the old lib/students.js.

- Tweak layout and styles to be more consistent and work better.

Navigated around and saw that everything worked as expected. Spent a bunch of

time making sure that layout was correct (previously some elements wouldn't

show the bottom @header-height of space when scrolling).