Implement -i, --inactivity-reset command line option
The use case is kiosk systems where leaving the application
idle for a period of time means that the user left, and the
session is reset so the next user starts off clean.
The implementation uses libXss and uses XScreenSaverQueryExtension
which means it is for now supported on X11 only.
Right now reset means closing any opens web pages and opening
the original web page.
Currently --inactivity-reset is only supported with --app.