Show only topmost property label for snakview in snaklistview

(bug 54317)
Since snaklistviews used for references and qualifiers feature snaks with the same property only,
the topmost label is displayed exclusively now.

Change-Id: I438839ef402c00695a8c312262cbfc7aff35f1f2
Merge "Show only topmost property label for snakview in snaklistview"