Improved Mac experience; QDoubleSpinBox for BitcoinAmountField

Now it can't be told if this is was a Windows App before. All Mac design principles are fulfilled and some cosmetics have been applied to suit the native look and feel. The biggest change there is the proper use of the Dock icon which takes the role of the Tray icon on Mac.

The QDoubleSpinBox improves entering of Bitcoin amounts, no two separate fields are required anymore. All functionality and validation effects have been retained; pressing the comma key will be internally translated to a period to keep it consistent throughout the application and eases entering in countries which use the comma as decimal separator.

Additionally, Notificator now supports Growl, Mac's native notification system. This is provided via Apple Script in order to avoid linking to Growl on compile time. Other changes involve encapsulation of Toolbar and Menubar creation, loading of Qt's own translation and some clean up.