Add Laptop Power checking

Checks if the systems backing up is a laptop then it will check for
power connected. Put this together from the following two web sites.

http://arstechnica.com/civis/viewtopic.php?f=19&t=1118530
http://apple.stackexchange.com/questions/53111/run-a-shell-script-when-s
witching-to-battery-power