OSX: Work on Playlist UI.

- Flushed standard OSX toolbar for custom toolbar similar to MainWindow.
- Flushed standard OSX table view for custom SongGridView similar to
MainWindow.
- Added toolbar icons for new/open/save. I think those IcoMoon icons
kinda suck (compared to the other ones), will have to look for different
flat icons.
OSX: Several files were missing from last commit...