Give preference to images for autogenerated thumbnails

[ajkiessl]

We select the last thumbnail from an array of thumbnail urls generated for collections and works when setting the autogenerated thumbnail. So, the last file uploaded will contain the thumbnail used. Since it is preferred that an uploaded image is used as the thumbnail, see if there is a way to give preference to images. The thumbnail urls should be attached to FileResource objects, where I believe you can determine the filetype/extension. This could help us identify if the thumbnail is for an image — or something else.