CORE-4719 Added App Group sorting to AppsViewImpl.

Added StoreSortInfo to the TreeStore in AppsViewImpl so that App Groups are sorted alphabetically, except for root groups, which will retain the order returned by the service.
CORE-4720 Filter App duplicates in grid listings.

Since an App may now appear in more than one category, the same App could be listed more than once in search results or parent groups.
Updated AppsViewImpl#setApps to only add apps that are not already in the ListStore.