Invalid imagery should be indicated as such in the browser

Currently, Invalid images (no desc and/or credit) do not indicate that fact in the browser. They may look like Free to use.

- [ ] they should get a red warning triangle badge and a corresponding tooltip (probably `Unusable: missing [description] [and] [credit]`
- [ ] they should also get a corresponding Info panel badge turn red (`x unusable`?)
- [ ] discuss if they should disappear from Free to use searches (but check if it’s easy to do)