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
Changed signature of IMvxViewModelLocator to throw an exception in case a viewmodel fails during creation or initialisation.
Merge pull request #838 from jesperll/Mvx837-ThrowExceptionsInViewModelLoader

Allow IMvxViewModelLocator to throw exceptions
Merge pull request #833 from lothrop/3.5

Fix import targets for Unified API