Something wrong with the binding

In 5.4.0 version the test passed
Merge pull request #556 from maratoss/patch-1

Something wrong with the binding
Fix finding DependencyProperties declared in base classes

Conflicts:
	ReactiveUI.Platforms/Xaml/WpfDependencyObjectObservableForProperty.cs
Fix this for WinRT too, in a more nightmarish way

Conflicts:
	ReactiveUI.Platforms/Xaml/DependencyObjectObservableForProperty.cs
Backport to RxUI5
Bump MonoMac Rx version to current version
Version bump to 5.5.1