Group similar transaction comments in Conpherence

Summary: Adds a CSS class if comments come in from the same user in the past 2 minutes for cleaner UI. Note will have to find some better display UI when comment editing comes.

Test Plan: Test lots of random Conpherence messages with different transactions, different people, and quick commenting.

Reviewers: scp, epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16632