Remove "Chaos" mode and fix fullscreen in Conpherence

Summary:
Fixes T3782. Two changes:

  - Remove the "Chaos" mode, which wasn't as funny as I'd hoped and has had a good run.
  - Fix "Order" (now "Fullscreen") mode in Conpherence. Best fix I could come up with is dropping the "position: fixed" on all parents while in the mode.

Test Plan: Used Fullscreen mode in Conpherence in Chrome.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T3782

Differential Revision: https://secure.phabricator.com/D6844