Added event handlers to Skip Track
Modified queue to store tracks to skip
Added skip track feature
Minor fixes and label adjustments
Greying out song and added verification to next on album mode
Renaming skip properties, strike out track when it is to be skipped
Merge branch 'skip_track' of https://github.com/asiviero/Clementine into asiviero-skip_track

Conflicts:
	src/playlist/playlist.cpp
	src/playlist/playlistitem.h
	src/ui/mainwindow.cpp