Call django.setup() as part of reviewboard.initialize()
Call django.setup() as part of reviewboard.initialize()

In Django 1.7+, there's a new `setup()` function which initializes logging and
apps. Attempting to do too much before this is called will fail with errors.
This change adds a call to that during our `initialize()` method.

Testing done:
- Ran unit tests on Django 1.6 and 1.8.
- Ran the devserver on 1.8.

Reviewed at https://reviews.reviewboard.org/r/8711/

davidt/reviewboard,davidt/reviewboard,chipx86/reviewboard,chipx86/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard,davidt/reviewboard,davidt/reviewboard,sgallagher/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,chipx86/reviewboard,brennie/reviewboard,brennie/reviewboard,brennie/reviewboard,brennie/reviewboard,reviewboard/reviewboard