Begin to extract the wiring between a sidebar and the content pane of
the template dialog booklet layout. Eventually, this helper class
will present a high-level interface like "addPart(id)" and will take
care of creating the outline item, content page, and connecting
events.
Start very simple, take over the "focus" method.
Bug: T284632
Change-Id: I7bc73cc4386b99d95941fc6ed88ab5bd998de014
