Feature: Interactions like in ReactiveUI

[fubar-coder]

Short description

It'd be nice to have a better separation between UI and the ViewModel by providing Interactions like those provided by ReactiveUI.

Use case

I stumbled upon the "problem" that I had to show a message box and wanted to set the parent window, which is not available in the ViewModel. IOW: I'd like to:

• Show a dialog
• Set the owner of the dialog
• Return the result of the dialog

Example

The view model should be able to create an instance of a Interaction<TInput, TOutput>, which the view must connect to, to do its interactive UI stuff. The Reactive UI documentation contains a description of the feature.