Bug 122850 Table/list should not be able to be inserted in Master Page mode.
Description: Table/list should not be able to be inserted in Master Page mode. Steps to reproduce: 1. New a report and transfer to Master Page mode. 2. New a datasource and dataset 3. Drag a list/table to page header/footer, bind it to dataset and drag some columns inside. 4. Save and preview Expected result: Insert list/table item in master page should be forbidden. Actual result: They are allowed and preview showed "undefine" in page
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* @param slotId
	 *            the slot id of the container element
	 * @param content
	 *            the target element to be inserted
	 * @return <code>true</code> if this insertion is valid. Otherwise
	 *         <code>false</code>.
	 */
	protected List checkContent( Module module, DesignElement container,
			int slotId, DesignElement content )
	{
		return new ArrayList( );
	}
	/**
	 * Checks whether elements with the given element definition can be inserted
	 * to the slot <code>slotId</code> in another element
	 * <code>container</code>.
	 * 
	 * @param module
	 *            the module
	 * @param container
	 *            the container element
	 * @param slotId
	 *            the slot id of the container element
	 * @param defn
	 *            the element definition
	 * @return <code>true</code> if this insertion is valid. Otherwise
	 *         <code>false</code>.
	 */
	protected List checkContent( Module module, DesignElement container,
			int slotId, IElementDefn defn )