Quicksand - make notification and message counts update as you navigate around

Summary: Ref T7573. Unify code to fetch these counts and do some light formatting since we're going to need to do the same thing for some conpherence-specific ajax in the durable column (See T7708).

Test Plan: loaded up two tabs, one with a durable column on and one without. in the without browser, i read some messages, decrementing my unread count. when i navigated again in the durable column browser, the count updated correctly. with no notifications, commented on a task with another user to get a notification and it showed up properly. visited the task by clicking not the notification and the bubble count decremented correctly

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7573

Differential Revision: https://secure.phabricator.com/D12498