Conpherence - fix some ajax bugs

Summary: the people widget was returning a comma-delimited list of HTML nodes so kill that noise with some hsprintf action. We also weren't consistently updating the latest transaction id so simplify those codepaths (widgets vs pontificate) a bit. Fixes T3336.

Test Plan: left some messages, added some participants. noted that the people widget looked good and only the pertinent transactions were pulled down on updates.

Reviewers: epriestley, chad

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T3336

Differential Revision: https://secure.phabricator.com/D6180