Implement order and chaos modes for Remarkup editing
Summary:
Ref T2599.
Implements an "order" mode which fullscreens the editor and reduces distractions, similar to Asana's "focus" mode and GitHub's "zen" mode. This can help users who need fewer distractions get work done.
Implements a "chaos" mode which does the opposite. This can help users who need more distractions to get work done.
Test Plan: Clicked "order" and "chaos" buttons.
Reviewers: chad, btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2599
Differential Revision: https://secure.phabricator.com/D5735