nicer file type search

Created by: dakkar

• the previous one could allow a SQL injection, since the opts.filetype value came straight from the browser

• this more precise regex match will not produce spurious matches (which were very unlikely, true, but still, let's be precise) (video/movingimages would have matched %image%!)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests