GeoNode/geonode — pull request #1884 by simod (2014-12-10 13:37:51+00:00)
Title: Thumbnail simple

This PR simplifies a bit the Thumbnail management.
Removes the Thumbnail class, a thumbnail is now composed by a file on disk and its associated Link.
Adds back the logic to include the background in the map thumbnail.
Moves the main thumbnail logic to ResourceBase.
Fixes a Layer metadata save to not save twice.
Thanks Ariel