Simplifying listview widget while introducing snaklistview

The generic listview widget does not need a cascading DOM structure anymore. The toolbar
placeholder needed for the references is moved to a new snaklistview template.
The actual snaklistview widget will be implemented in another change set.

Change-Id: Id2cbff8246baba9dad93e35a0dd1ff9cc1f9cbdf
Merge "Simplifying listview widget while introducing snaklistview"