Change of the track color for the dark themes

The track number was not visible while the row was not selected, now it
is visible.
Preliminary work for a Yosemite style
Spotify Black style for Yosemite
Add Yosemite extensions for remaining styles
Enable Yosemite style only for 10.10 and above
Proper hiding/showing of Yosemite toolbar
Yosemite visual tweaks
Fix separate cookie storage for OS X 10.10 (and possibly 10.8)
Fix mini-player to re-use background image in large mode
Fix/update status menu item to work with dark mode
Fix bug that always used star rating system instead of thumbs
Fix window height, cleanup popup display
Yosemite visual tweaks
Tweak search button in Yosemite theme
Make Yosemite changes backwards compatible
Yosemite backwards compatible mini-player drawing
Merge pull request #230 from kbhomes/yosemite

Yosemite support
Merge pull request #198 from Gta-Cool/master

Change of the track number color for the dark themes
Yosemite: make mini player use dark mode when system is in dark mode
Yosemite: tweak to fix wrong mini player icon colors on startup