[NbtkPopup] hide the popup if the user clicks outside the menu
[NbtkPopup] hide the popup if the user clicks outside the menu

Capture events from the stage when the popup is open and check if they
fall on the popup of its children. If the event is outside the popup then
swallow the event. If the event is outside the popup and is a click event
then close the popup.

pwithnall/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx,jonnylamb/mx,clutter-project/mx