Fix for acceptance test static file issue

Recent changes to how we start up django apps broke lettuce tests.

1) Previously, we replaced django.contrib.staticfiles with django-staticfiles to satisfy both lettuce (uses the built-in library) and mitxmako (uses external library).

2) Changes to how we initialize Django apps caused django.contrib.staticfiles.handlers to no longer point to django-staticfiles.handlers.

3) This PR replaces django.contrib.staticfiles.handlers explicitly to avoid this issue.

@jzoldak