Restore "Unbreak Now" and "Needs Triage" homepage boxes as cusomizable elements

Summary: Ref T3583. Fixes T3835. Dropbox and Disqus both want these things back, so restore them until we can do something about T3583.

Test Plan: Viewed homepage, clicked "View All X" buttons.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3583, T3835

Differential Revision: https://secure.phabricator.com/D7017