Fix the admin site only showing OAuth-related models
Fix the admin site only showing OAuth-related models

We were accidentally importing the `reviewboard.oauth.admin` module too
early, causing `admin.autodiscover()` to never be called (because we had
already registered our `Application` model). This was leading to only
`oauth2_provider` and `reviewboard.oauth` models being shown in the
admin site DB page. Importing the admin in a function scope fixes this
issue.

Testing Done:
With this patch applied, models get registered correctly.

Reviewed at https://reviews.reviewboard.org/r/9058/

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