Manual notification close function

[ud-waffle]

For my project I required a function to manually close a specific error notification, so I've decided to implement it and create as well a visual/testable interaction in the Wpf.Sample project (as shown below).

As I think this might be useful for everyone if the dev gives me branch creation permissions I'll push my version, to a separate branch.

[majsterkoo]

I think, that you can fork project, push changes and then create new pull request?