Conpherence - improve performance by handling dropdowns (notifications, threads) as standard response data

Summary: Ref T7708. Rather than invoking the general client -> server dropdown refresh path, return the data with the various conpherence requests and update the dropdowns that way. Saves 2 client -> server requests per conpherence action.

Test Plan: loaded up /conpherence/ and noted message count deduct correctly. clicked specific message and noted message count deduct successfully. did same two tests via durable column and again saw message counts deduct successfully.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7708

Differential Revision: https://secure.phabricator.com/D12761