Conpherence - kill the image-based header UI

Summary:
removes the whole custom image thing, instead using a more standard application crumbs. Gives this glorious space back to the compose area which is now tens of pixels taller. Also defaults it to the people widget. Basically, fixes T3160.

For now, you **CAN NOT** edit the title of a conpherence. I didn't want to jam in too much here. Next diff will be to change the widget icons into the dropdown switcher, which will also bring back the editing of titles.

Test Plan: looked at conpherence and it was pretty. Resized it vigorously and it wasn't too bad.

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Maniphest Tasks: T3160

Differential Revision: https://secure.phabricator.com/D5998