Multiple toasts stacking and moving

[cuken]

I may be missing the functionality, but having the ability to send multiple toasts to a region on the screen and have them stack in a direction relative to each other. Then as toasts disappear have the remaining toasts move in the direction to fill in the void.

[zachatrocity]

This is desired functionality that is not yet implemented. I haven't been using WPF in awhile and so I haven't had a need for this tool. Please feel free to submit a pull request!