Admin can directly upload images, and can optionally upload them to Flickr

- [ ] additional model (structure?) for images, optionally linked to Flickr image (essentially, #19)
- [ ] upload for admin, several files at once
- [ ] initial edit of meta information
- [ ] optional further upload to Flickr (with selectable resolution)
- [ ] downscaling with ImageMagick where appropriate, with Flickr-style file name suffixes for gallery plugin
- [ ] link to Flickr configuration for adding freshly uploaded pics to sets, groups, etc.