This is a simple script that watches the current qube for idleness and, if it's idle for more than 15 minutes, 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).