go to sleep when lid is closed and docking station removed

I created #203 , but a reverse workflow scenario also needs to be considered. You already have your computer plugged into a docking station and the lid is already closed. You work for a while and then are ready to go. When you unplug the dock cable, the computer should be able to realize that it's time to go to sleep because (1) there is no external power but the battery, (2) there is no graphics displayed, and (3) there is no keyboard and mouse to use. I would say in 99% of use cases, people are going to want their computer to go to sleep when this happens. Right now I need to wait 15 minutes in order for the system to go to sleep because of a normal idle on battery power case.