Bug 123406 Add geLocaltStringProperty in GroupElementHandle and GroupPropertyHandle
Please refer to 123405. GUI need a way to get the local setting of given property because current getStringPropery method will return inherited value if there are no local value.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/GroupPropertyHandle.java
{
	/**
	 * Definition of the property.
	 */
	protected ElementPropertyDefn propDefn = null;
	/**
	 * Handle to a collection of elements.
	 */
	protected GroupElementHandle handle = null;
	/**
	 * Constructs a handle to deal with an common property within a group of
	 * elements. The given property definition should be a common property
	 * shared by the collection of elements.
	 * 
	 * @param handle
	 *            Handles to a collection of elements.
	 * @param propDefn
	 *            definition of the property.
	 */
	GroupPropertyHandle( GroupElementHandle handle, ElementPropertyDefn propDefn )
	{
		assert propDefn != null;