reviewboard.site.tests was getting a bit big, covering many areas of

Local Sites. With some new tests coming, it seemed time to split this

up.
This creates a series of new test cases for different areas of the app,

moving tests into them. The tests themselves have not changed, aside

from the removal of the old import reviewboard.site.templatetags hack

for our {% url %} replacement, which is not needed with modern Django

template configuration.
One test for managing OAuth2 Application access when Local Site

membership changes has been moved into reviewboard/oauth/tests.py.

Unit tests pass.