R1:dd9ec255ecac

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…