Conpherence - make empty comment submission behave like other apps

Summary: now we get a "you can't submit no text" error. Also puts the participant status updating inside the editor.

Test Plan: made empty comments and got the right error dialogue. made legit comments and they went through. made a new conpherence - work. edited title + picture on old conpherence - worked. tried to submit non-updates to title and image - correct error.

Reviewers: epriestley, chad

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2419

Differential Revision: https://secure.phabricator.com/D4734