Automatically sort favorited items up top in a folder view

[jancborchardt]

Currently marking as favorite only adds an indicator in the list view and you need to manually switch the view to go to all favorited items.

To have favorites more present, we could experiment with automatically having the favorite files of the current folder sorted up top in the view (subfolders and files immediately in there, not recursive of course).

cc @karlitschek @PVince81 @DeepDiver1975 @LukasReschke this is also about the topic of ownCloud showing more relevant info to people. A bit related to #10788 (remember changes to sort order, sort by modified date).