R1:bd0a4c0d0416

Differential Updates View

Summary:
This adds a new view to differential called Updates.

The high-level goal of Updates is to enabled differential to be
effectively used without email notifications. I've tried doing things
like automatically deleting differential emails where I'm in the 'to'
line since they show up on the main diffential page but then there's
always the chance an important diff flies by without me seeing it. Also,
sometimes someone comments on a diff post-commit but differential
doesn't…