Add Menu entry in file list to optimize already existing images

[kaystrobach]

Make it possible to optimize images already registerd in FAL.

use case:

• old images

vision:

• optimize images already existing.
• use fal replace function to exchange existing images

[christophlehmann]

You can use something like find fileadmin -name "*.jpg" -exec jpegoptim --strip-all -q -p {} + to post-process old images

[kaystrobach]

I know ... but this would require an fal rescan afterwards

[christophlehmann]

That's okay. PRs are welcome.