Volume controls

Implemented a few features for controlling the iTunes app volume :sound:
I'm sorry but I'm not really familiar with Travis CI, but I think the problem is because of **osascript** tool which obviously doesn't exist on linux (where CI is currently building).

![schermata 2014-11-09 alle 17 22 24](https://cloud.githubusercontent.com/assets/1325491/4967992/ead9bc2c-682c-11e4-80a4-77c4a666ace6.png)