Fetch more: framework updated to fix TV grid and vertical list

The TV views did not properly update themselves when new items were
added to the underlying list because they had no real way to know
when the new children were rendered. The new "render:children" event,
trigger by the List view, makes it now easy to detect when rendering
is over.

Related feature in Pivotal:
https://www.pivotaltracker.com/story/show/45390535