Allow Dashboards to set an icon
Summary: Allows users set an icon (for reuse on upcoming home) for their dashboard based on 16 descriminating choices.
Test Plan: Create a new dashboard, set new icon. Edit an existing dashboard, set icon.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D17042