Make the ReferenceView have a ListView, instead of being one

ReferenceView was the only widget which inherited from ListView, instead of
having an instance of ListView.

Switching to the latter makes the codebase more uniform. Also, it's
conceptually more correct since the reference view actually consists of more
than just a list -- it also has a heading (and a toolbar).

This change is a prerequisite for the patch addressing bug 62527.

Change-Id: Id51603ae20c83175cdda78a5f2fa51eca887c367
Merge "Make the ReferenceView have a ListView, instead of being one"