Expose some JavaScript resource models and make them more useful.

This moves Repository and associated models into the 'common' bundle, so
that they can be used outside the New Review Request page.

It also adds rspNamespace fields to Repository and ReviewGroup, allowing
them to successfully parse payloads from the server.
Fix the order of validateDiffModel.js in the media bundle.

My previous change placed validateDiffModel.js too high, resulting in
errors on some pages. This moves it lower.
Use siteconfig_settings for settings access.

We had hacks around the templates for falling back on defaults if
settings were missing from siteconfig. This was missing in some cases,
and resulted in breakages in the case of displaying gravatars (a recent
change).

Djblets now provides siteconfig_settings, which allows access with
falling back on defaults. This change updates all templates to use it.

Reviewed at https://reviews.reviewboard.org/r/5694/
Fix the state of our JavaScript unit tests.

Our unit tests have regressed a bit recently, for a few reasons.

First, we were still trying to run the old configForms code, which
shouldn't have remained in the codebase. This has now been deleted, and
the new djblets-js-tests bundle has been loaded in to run the proper
configForms test suite.

Second, the recent addition to confirm the Discard Review Request action
resulted in the confirmation dialog appearing during the test run. We
now spy on window.confirm and provide a proper result in order to
prevent this.

Reviewed at https://reviews.reviewboard.org/r/5700/
Merge branch 'release-2.0.x'