(bug 45159) Introducing snaklistview widget

The snaklistview widget will manage multiple snaks by using a listview widget.
The snaklistview's first use is in the list of references. This change set is
only the first iteration that resolves the referenceview's inheritance by
defining the new snaklistview widget as parent instead of the claimview widget.

Change-Id: I25f64517f5c7d98b330f4d6a5620b7f62280de4d
Merge "(bug 45159) Introducing snaklistview widget"