Preload new topic

Authored by SBisson.


Preload new topic

URL parameters can be used to preload new topic
title and content on a flow board. This was broken
when the new topic handlebar template was replaced
by a widget.

Adding browser tests to detect regression in the future.

Bug: T112037
Change-Id: I183757cc5e3ed2f1340ba3f425dbc534bdbc86f0