Simplify logout view.
Instead of using django.contrib.auth.views.logout with a next_page of our login

URL, use django.contrib.auth.views.logout_then_login, which does the same

thing. Additionally, move the URLspec from reviewboard/urls.py to

reviewboard/accounts/urls.py.

Ran unit tests
Logged out of my devserver and saw that I was sucessfully redirected to the

  login page.