Bug 120218 Right click menu option to apply theme.
We should support the following right click menu. -- User right clicks int he report design layout area. -- The following menu items needs to be supported Theme --> Apply Theme -->Theme1 -->Theme2 ( similar to Apply style menu option )
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
assert child instanceof DesignElementHandle;
		int slotID = ( (DesignElementHandle) parent ).findContentSlot( (DesignElementHandle) child );
		return slotID;
	}
	/**
	 * Get the slot id of child If the slot id was not found, returns the
	 * default slot id
	 * 
	 * @param parent
	 * @param child
	 * @return slot id
	 */
	public static int getSlotID( Object parent, Object child )
	{
		assert parent instanceof DesignElementHandle;
		int slotID = -1;
		if ( child != null )
		{
			slotID = findSlotID( parent, child );
		}
		else
		{
			slotID = getDefaultSlotID( parent );
		}
		return slotID;
	}
	/**
	 * Find the position of the element. If the element is null, the position is
	 * last
	 *