Fix kdeconnect_open MimeType
This changes the MimeType handler of the kdeconnect_open desktop file from an invalid "*/*" to the (hopefully) appropriate "application/octet-stream;" as discussed [here](https://bugs.launchpad.net/ubuntu/+source/kdeconnect/+bug/1878400)(including this solution), [here](https://github.com/clearlinux/distribution/issues/1906) and [here](https://bugs.archlinux.org/task/65865).