R1:4fc37c3dde6f

Add diff view for Maniphest Task "description changed" transactions

Summary:
use the handy DifferentialChangesetParser to do most of the heavy lifting inside
the pertinent view object. update the controller to be aware of the "show
more" calls coming from the new ui and update the transactionID appropriately.

also snuck in a small change to AprontRequest to all getting all the request
data. I used it to debug building this.

Test Plan: made a task and entered a bunch of test data. had descriptions of…