When I change an App significantly, its Gallery entry should get updated

(User Story, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Apps
Summary: "Significantly" is any of the Properties in _App Gallery Entry; these should have a meta-Property on them so that the system knows to propagate changes to the Gallery.
This should only happen iff the App has been entered into the Gallery.