Add [Preferences],updated signal that lets other parts of Mixxx know when the preferences dialog has closed (and likely changed a preference). IMO this is prefereable to adding an individual signal for every preference option that might change (e.g. how the time-remaining widget works now).
Merge branch 'master' into features_key

Conflicts:
	src/dlgpreferences.cpp
Update WKey when preferences change since key notation may have changed.
Fix unused warning.