Added the autoconnect command

I found a question on [StackOverflow](http://stackoverflow.com/questions/20470626/python-script-for-raspberrypi-to-connect-wifi-automatically/21164401#21164401) asking how to scan and connect automatically to a network.  I responded to it and I wrote a tiny script to do that.  I think that we could include this script in the wifi command, it seems like a nice feature.