layouts and containers should not take menupopup into account when computing padding

<zk>
	<vlayout style="background:gray;">
		<label style="background:cyan;" value="no bottom padding" />
	</vlayout>
	<vlayout style="background:gray;">
		<label style="background:cyan;" value="bottom padding due to menupopup" context="someMenuPopup" />
		<menupopup id="someMenuPopup">
			<menuitem label="Some Action" />
		</menupopup>
	</vlayout>
</zk>