Improve user-experience on Mac OS X

We doesn't have much Mac OS X feedback since mostly users tend to use iTunes or any other media player.

• Look at features we are missing from iTunes (a lot, but mainly iPod support and Podcasts I would say)
• Make a native theme to integrate better with the system
• Allow user to select Nightingale as default player
• When we reach XUL15, look at new features supported for Mac OS X such as retina

• Test Nightingale and detect bugs
• Look for SB add-ons made for Mac OS X and maybe integrate some ?

• #52 Default player on Windows/Mac
• #107 Mac native title bar