Don't initialize Review Board when creating database models.
Don't initialize Review Board when creating database models.

In a development environment, running `manage.py syncdb` would call
`initialize()` before creating database models. If any code in an
initialization signal handler tried to access the database, and the
database was empty, syncdb would crash.

We no longer call `initialize()` for this command. We fortunately don't
call it when doing `rb-site install`, meaning both that there's
precedent for avoiding the call and that this problem doesn't impact
production at all.

Testing Done:
Tested `syncdb` with and without a functioning database.

Tested all other affected commands: `test`, `runserver`, and a few
other management commands.

Reviewed at https://reviews.reviewboard.org/r/10069/

reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard