Generate thumbnails of image uploads #89
Description
Generate automatic thumbnails of uploaded images.
It would be a good idea to let the dev define the thumbnail dimensions and cropping method, and with similar effort define multiple thumbnail sizes per upload.
Less clear is whether the dev should be able to define the thumbnail setup per file field, or globally? The former would definitely need to happen in the model, while the latter would happen in config.json - would it be confusing to have multiple locations for this?