Adds a GeoView controller to help with common MVVM challenges

[dotMorten]

Helper class for allowing you to perform view operations on the MapView from your ViewModel, through an attached proxy-object that ensures you keep VM and View separated.

Design choices:

• Basic controller for most common operations like setting viewpoint, performing identify and showing callouts. No specific mapview or sceneview operation.
• Extensible, so you can add your own custom map and scene operations, or interface for allowing testing (see WPF sample)
• No events exposed - use EventToCommand or similar already established approaches to forward view events back to the view model (see samples)