Handle mime-types
When clicking on an vnc://ipaddress or rdp://ipaddress, users should be prompted to open Connections.
To do this we need:
- Add the supported mime-types to the MimeType keyword in our desktop file.
x-scheme-handler/vnc;x-scheme-handler/rdp;
- Teach Connections how to handle arguments passed to it. See https://valadoc.org/gio-2.0/GLib.Application.open.html