libsoup2 is phasing out, and using it in a plugin causes conflicts with
other plugins using a newer version, including ones using a current
webkit2gtk.

Also, properly abort pending requests when unloading the plugin, in the
unlikely case they didn't all finish by that time.

Not only should this be in the German translation if need be, but I'd
also just not use quotes after a colon.

There are very little HTTP needs, so GIO with an HTTP VFS
implementation, which is usually available.

This fixes the libsoup2 vs libsoup3 issue as well.