Clean up random junk in Conpherence

Summary: Fixes T10781. Re-uses sidenav styles from global space, though a little hacky. Fix crumb border, fix nux experience. Fiddle spacing.

Test Plan:
Use Conpherence as new user, make a room, post some messages.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T10781

Differential Revision: https://secure.phabricator.com/D16528