Update GroupForm and DefaultReviewerForm for LocalSiteAwareModelFormMixin.

Review Request #10366 — Created Dec. 27, 2018 and submitted — Latest diff uploaded

Information

Review Board
release-3.0.x
aaa704f...

Reviewers

This updates both GroupForm and DefaultReviewerForm to use the new
LocalSiteAwareModelFormMixin, providing automatic validation of
related objects and the ability to limit choices to a LocalSite. This
simplifies the forms a bit and expands the testing and security of the
forms.

Error messages have also been updated for the various related fields,
providing more useful, contextual errors. Future changes will help make
these even more consistent across forms.

Unit tests pass.