Conpherence - add an updatethread conduit method

Summary: Last of the methods. Fixes T3166.

Test Plan: updated a thread in all the various ways except remove and it worked. removed myself and it worked! tried to remove someone else and it yelled at me.

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Maniphest Tasks: T3166

Differential Revision: https://secure.phabricator.com/D6103