update layer-shell protocol to version 4

Tracking with breaking change from swaywm/wlroots@b7dc4f2.

Merge updates from guidocella

Thanks so much for helping to keep the project running while life was
crazy!

Merge pull request #49 from guidocella/layer-shell

Layer shell

Implement the idle protocol

It allows clients such as swayidle and chat applications to monitor user
idle time.

layer shell initial attempt