Compatibility with Karabiner-Elements on macOS

[jace]

Using DeskHop with Karabiner breaks mouse movements (originally reported there: pqrs-org/Karabiner-Elements#4252). I want to remap PrtSc to Cmd+Shift+5 so I have the same physical key between Linux and macOS, pending a built-in HID remapping solution as discussed in #84.

I think the problem is caused by how Karabiner works -- replacing a HID device with its own virtual HID device -- which seems to be breaking how it processes DeskHop mouse coordinates. It may help if DeskHop reported to macOS as separate keyboard and mouse devices (like on Linux) so Karabiner can override only the keyboard.

[jace]

I tried configuring DeskHop to OS as Linux. Karabiner still saw two HID devices for K+M and M-only, while multi-screen support broke. Back to macOS mode.