Allow a dialog webscreen to show over top of a normal webscreen.

Allowing a dialog webscreen to be displayed over top of another webscreen would allow a "submenu" type interaction.  A dialog feels more like a natural UI element than an overlay screen. As of now the original normal web screen is completely replaced with a full screen dialog when the dialog is created. 

Assigning the screens overlay IDs does not have any effect since neither screens are overlays.