adding IMvxNotifyPropertyChanged extension methods to simplify notification property setters

e.g., this.RaiseAndSetIfChanged(ref _hello, value, () => Hello);

Based on the work of paulcbetts in the reactiveui project
See https://github.com/reactiveui/ReactiveUI/blob/rxui6-master/ReactiveUI/ReactiveObject.cs
Added UIStepper to LinkerPleaseInclude-file

UIStepper would sometimes be stripped from the assemblies so bindings
would fail on the Value property.
Added UIPageControl to LinkerPleaseInclude-file

UIPageControl would sometimes be stripped from the assemblies so
bindings would fail on the Pages property and the ValueChanged event.
Added in the ability to raise property changed based on the calling property.
nuspec changes - 3.5.0 alpha2
Refactor to enable #835 to occur outside of Mvx
Merge branch '3.2' of github.com:rossdargan/MvvmCross into 3.5
Merge branch '3.2' of github.com:PelleRavn/MvvmCross into 3.5

Conflicts:
	nuspec/TouchContent/LinkerPleaseInclude.cs.pp
Merge branch 'RaiseAndSetIfChanged-Extensions' of github.com:patsissons/MvvmCross into 3.5