WinRT fundamentals - IObservableVectorView and IObservableMapView

[jaigak]

microsoft/xlang#789

Currently WinRT lacks read-only versions of IObservableVector and IObservableMap - making it impossible to expose an observable collection that should now mutated from the outside.

[jaigak]

Technically, as IObservableVector and IObservableMap do not inherit from IVector and IMap respectively but only require it (as interface inheritance is unsupported in WinRT), it should be possible to have a class that implements these without implementing IVector or IMap and instead only implementing IVectorView and IMapView.

This is not a great solution, however, since users who get an IObservableMap or IObservableMap would expect to and will probably query for IVector or IMap, which won't work.