Basic user account support

Allows logging in using Facebook (with other providers easily available) at the `/account` URL.

**Notes**
User edit and deletion in the admin panel is supported, although any user's data that is edited in the backend is overwritten with their Facebook data on next login. Can be fixed with more 1s and 0s.

Deletion doesn't handle removing the user's cookies (obviously). Also doesn't remove their auth tokens (gotta fix that, too).

This does not use the user model that we defined in a file, but instead uses webapp2's Expando-based user model.

Whitelist is setup to pull from the `auth.whitelist` sitevar with a JSON dict of authorized IDs.
Ex: `{"100001996614213", "100005694099700"}`