Added PropertyChangedEventArgsExtensions.HasPropertyChanged with string override
Minor improvement in PropertyHelper
(x) CTL-351 CommandManager throws NullReferenceException on KeyDown when no KeyGesture is registered
(+) CTL-352 Allow Action to be registered besides ICommand in the CommandManager
(+) CTL-353 Add generic overloads for UIVisualizerService.Show and ShowDialog
(+) CTL-354 Introduced UserControl.UnloadBehavior to specify the behavior which will be handled when the view is being unloaded or the data context changes
CTL-354 Updated default value of UserControl.UnloadBehavior to SaveAndCancelViewModel
Merge branch 'develop' into feature/CTL323_ApiCop

Conflicts:
	src/Catel.MVVM/Catel.MVVM.NET40/Windows/Controls/MVVMProviders/Logic/UserControlLogic.cs