User-level form assignments

[aclark02-arcus]

Similar to how users can select Region / Sites to review, it would be nice to allow users to select only the forms they are responsible for reviewing in Settings. That way, if someone isn't responsible for a particular form, it doesn't show up in their queue. I think the form should still be accessible / available just in case they need to peak at it, and they can still review it if they want to (or if a colleague is OOO), but not required.

This is kind of related to #22 and #43.

[LDSamson]

Maybe we can implement this by creating a user_settings table in user_db.sqlite, in which we can save the desired settings. In here, we can also save the sites selected by the user.