collections browser , enhance with thumbnails

in the 'public collections' screen, it would be nice to show a few images from the collection, to give more of an idea whats in there, and perhaps some of the existing labels used in it
(perhaps show the most common labels, and the most-labelled images)

Start at the public collections screen and trace how collection images and labels are currently loaded and rendered. Define a small representative set of thumbnails and commonly used labels, then verify that the screen gives visitors a useful preview of each collection.

Written by the indexing model from the issue text.