Small Prism projects structure improvements
Merge branch 'feature/CTL290_Prism' into develop

Conflicts:
	src/Catel.Extensions.Prism/Catel.Extensions.Prism.NET40/MVVM/Services/Extensions/ISplashScreenServiceExtensions.cs
	src/Catel.Extensions.Prism/Catel.Extensions.Prism.NET40/MVVM/Services/Extensions/IUIVisualizerServiceExtensions.cs
	src/Catel.Extensions.Prism/Catel.Extensions.Prism.NET40/MVVM/Services/UICompositionService.cs
	src/Catel.MVVM/Catel.MVVM.NET40/Services/Interfaces/IUIVisualizerService.cs
	src/Catel.Test/Catel.Test.NET40/Extensions/Prism/UIVisualizerServiceExtensionsTests.cs