Conpherence - auto focus the textarea on thread select and after sending a message

Summary: Fixes T7135. Also does a bit of a javascript cleanup in that we had an event - "conpherence-selectthread" - which really didn't need to be an event.

Test Plan: selected various conpherences from the list and they loaded correctly, including putting the cursor at the end of the text as appropriate. send many messages rapid fire without ever taking my hands off the keyboard.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7135

Differential Revision: https://secure.phabricator.com/D11890