Added XAML markup attributes, namespace mappings and custom collections types to implement design time compatibility (MP2-454)
Renamed *MarkupExtension to *Extension, so XAML is able to find them (MP2-454)

Conflicts:
	MediaPortal/Source/UI/SkinEngine/MarkupExtensions/MultiBindingExtension.cs
Adding assembly name to make sure that controls can be referenced from other assemblies (MP2-454)
Minor cleanup
Added MPFExtensionBase to derive all MPF extensions from (MP2-454)
Added WPF wrapper for MPF converter (MP2-454)
More WPF-XAML compatibility (MP2-454)
New specialized collections (MP2-454)
New specialized collections (MP2-454)
New specialized collections (MP2-454)
Added basic dialog and button style