Conpherence - add draft support to column and refine sending message user workflow

Summary: Ref T7014. This diff adds draft support.

Test Plan: made many comments and they submitted nicely.

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7014

Differential Revision: https://secure.phabricator.com/D12046