We need to send messages to the parent so that we don’t set up an
infinite loop by sending `tw-navigate` messages. Also we need to pass
along the target of the navigation.
Getting rid of the old widget mechanism files finally gives us a payoff
for all the refactoring. Still a bit of tidying up to do, and we need
to re-introduce the animation mechanisms.
Get rid of the separate renderContext stack and instead have a parent
pointer on renderer nodes. This lets us walk back up the render tree to
resolve context references
