[Phone Connect] Add remote control support

[ComputerElite]

I'm really enjoying DMS so far. I'd support for mouse movement and keyboard input from Kde connect as I tend to use these on a regular basis for my theatre setup. I'd also be willing to try and implement it.

[nojvspine]

afaik kde connect uses Remote Desktop portal for remote input, and it's usability depends on a specific portal implementation used
I've tested it with all existing portals aside from kde one (gnome and luminous) and was unable to get it to work
someone needs to test it with xdg-desktop-portal-kde and if it works, report an issue to gnome and luminous portals, or, if it doesn't, to kde connect
I don't think DMS could do anything about this other than develop their own portal implementation