No recentchange entry inserted for new topics

The lifecycle handler to insert recentchange entries
for all newly inserted posts was failing due to it
being unable to find the related workflow.

The workflow itself was set to be the last item to insert
on new topic creation in e2ce5191532308aa2101de115b83f87a7f1af8e9
to fix another bug, but that created this bug.

This time arround use DeferredUpdates to allow all the inserts to
happen and then do our housekeeping later in the request.

Bug: 68412
Bug: 68848
Change-Id: Ife7c3e169782f2b162363520b0e68ee80b8dc115
Merge "No recentchange entry inserted for new topics"