HEAD (or other approach) links to fetch Content-Type for video/image preview

[chinese-soup]

• ... and therefore determine whether to show the Preview button or Open the preview (if "open link directly" option=true)
• Should probably be an option, also, since some people don't like giving out their IP to a server without actually opening the link.

Current state:

• Currently a primitive URL.endsWIth(".jpg") etc. is used which doesn't apply to a lot of links that are images/videos just by Content-Type and not by filename. (E.g. https://pbs.twimg.com/media/Eni5KRUXEAUg2tE?format=jpg&name=small)

This could also be used for a limit of Content-Size that is allowed to be (which could be an option) previewed in the app. (Since .e.g a 500 MB video file might not be a good idea to open in Qt? (just guessing, dunno, really))

Cons of HEAD:

• Slower
• HEAD can be disabled/unsupported on the destination server, fallback to endswith(".jpeg|.jpg") etc. then

Any other ideas?