This is a simple script that watches the current qube for idleness and, if it's
idle for more than 15 minutes (timeout time is defined in
qubesidle.idleness_monitor), shuts it down.
At the moment, only checking for visible windows is supported - when a VM has no
visible windows for more than 15 minutes, it's going to be shut down. The
mechanism is opt-in - enable shutdown-idle service in qube settings to use it.
If needed, other watching methods can be added: check the qubesidle Python module for details (in brief: all you need is a Python module supporting a couple methods).