Make Conpherence Pontificate Send-on-Enter

Summary: Fixes T11623. Enables send-on-enter and shift-enter for linebreaks, per durable column. Also cleaned up UI for Joining Room or Logging In.

Test Plan: See room I can join, click Join Room. Leave Room, Log out, visit room with login prompt. Login, Join Room again.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11623

Differential Revision: https://secure.phabricator.com/D16595