Apront Two Column View
Summary: Wanted to pull this out in case we don't use it in Maniphest, still useful perhaps in the future. Creates a sidebar that wraps when on mobile.
Test Plan: Tested UIExample
Reviewers: epriestley, btrahan
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D5321