GalleryPicker Dialog for uploading with categories code review

I've implemented direct uploading with the gallerypicker. This works perfectly.

When i've tried to added the categories (imagesets) dowpdownbox (supply patch), the UI of the thumbnail view doesn't work properly, selecting items doesn't give the impression that the item is selected while it is.

I think this has to be fixed in de linkdialog or thumbnailview rather than in the gallerypickerplugin

affects 1.09.00(-SNAPSHOT)