Growl notifications

I added this by cloning most of the Prowl options and adding the GNTP library. I tested it briefly for local and external growl receiver, and it works. That said, it's implemented rather quickly :-)

![schermafbeelding 2014-04-01 om 00 36 46](https://cloud.githubusercontent.com/assets/815976/2573798/87dd728c-b925-11e3-8fc1-b12948976c86.png)

This fixes #239 and #1347