Add tests for new models and banner creation process.

Also fixes issues with existing tests:
- Jenkins runs Python 2.6, which doesn't support using assert_raises as
  a context manager, so we use Django's version on TestCase, which uses
  the version from unittest2, which does support it.
- Set BannerFactory to be an abstract factory.
Add link referral view that sends data to GA and use it for banner code.
Add management command for retrieving referral data and fix model.
Tests!
Add google-api-python-client.
Add setting for stylus support.
Base template, stubbed out home page
Bug 976231 - leaderboard template

With a few base changes, too
Merged before Craig could fix the capitalization, doh!
Install pytz.
Enable timezone support and set default timezone to UTC.

Also fixes instances that were using non-aware datetimes.
Store the type of banner that links were created by.
Bug 976782: Calculate and display milestones.
Tests!