This introduces a new concept for extensions and users, User Details

Providers, implemented as subclasses of UserDetailsProvider. This is

a class that can build upon to let exetnsions provide additional

information about users without needing to worry about extending User,

Profile, or implementing whole new hooks.
UserDetailsProvider subclasses can be registered in a central registry

and then implement methods to provide certain kinds of details that

Review Board can then query for additional functionality.
Right now, these can provide badges for users. Badges are shown

alongside a user's name in certain parts of the UI (infoboxes and

discussions, currently). They contain text and may contain custom CSS or

even custom HTML.
This is purely built for extension authors to take advantage of, giving

companies greater control over Review Board.

Unit tests passed.
Tested with an extension that added some hard-coded badges. Verified these

showed up in reviews, discussions, and infoboxes.