Conpherence - add tooltip for full time for messages

Summary:
Fixes T8154. Now you can tell when a Conpherence was started by mousing over the date. I think this is sufficient.

This ends up cleaning up the code significantly; it used to inherit from some transaction view class and had built up lots of cludge over time. Much cleaner now.

Test Plan: moused over tooltips in both durable column and full conpherence and saw correct full dates. clicked on a timestamp in durable column and went to right place in full conpherence.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8154

Differential Revision: https://secure.phabricator.com/D13057