Update to use umbOverlay

[mortenbock]

Hi Tim

I learned from the mediapicker example, but it looks like the dialogService way used in this sample is deprecated in favor of the umbOverlay directive: https://our.umbraco.org/apidocs/ui/#/api/umbraco.directives.directive:umbOverlay

:)

[TimGeyssens]

Ah thanks for the heads up! Yeah could use an update :)