Fixes to topic editing

* Avoid creating duplicate edit topic forms. When clicking edit title,
check whether there is an existing form. If there isn't render it.
If there is simply refocus it.

* Fix bug with nested flow-topic.

* Change submission logic for title to only re-render titlebar.

Change-Id: I71e307c3cf9044d208a11df27586748f4b98e98d