Cocoa: Fix beep-on-show for Creator menus.

Cocoa: Fix beep-on-show for Creator menus.

Maintain a current window state variable in QCocoaWindnow
and use it when setting the new window state on the
NSWindow.

The NSWindow state accessors can apparently not be
trusted, in particular isZoomed always returns true
for the Creator popup menu.

Change-Id: I78f13de251f3730752813bba17459011f8558aee
Reviewed-by: James Turner <james.turner@kdab.com>
Reviewed-by: Christoph Schleifenbaum <christoph.schleifenbaum@kdab.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>