Enable using hotkeys to lock the current screen

[timgws]

Enable using hotkeys to lock the current screen/not send glide commands to the server.

[timgws]

This is relatively easy to implement. Register a global hotkey with the OS, and then set switching = true. This will stop the commands from being sent by the client to the server - effectively pausing switching.

Some logic will need to change on the websocket handler, because currently it will set switching = false when it sees that another client has sent a command to switch desktops.