Also list subclasses

[phil294]

Hi Martin, thank you for this useful tool.

Subclasses seem to be missing, for example, inode/mount-point (see /usr/share/mime/inode/mount-point.xml) is missing in both selectdefaultapplication and in mimeapps.list, but it is listed e.g. in xfce4-mime-settings (and /usr/share/mime/subclasses). Shouldn't these also be included?

(coming from https://unix.stackexchange.com/a/528460/103120)