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/GroupElementHandle.java
for ( Iterator iter = elements.iterator( ); iter.hasNext( ); )
		{
			DesignElementHandle elementHandle = (DesignElementHandle) iter
					.next( );
			if ( elementHandle.getElement( ).hasLocalPropertyValues( ) )
				return true;
		}
		return false;
	}
	/**
	 * Checks whether a property is read-only in the property sheet. The visible
	 * property is read-only in all <code>elements</code>.
	 * 
	 * @param propName
	 *            the property name
	 * @return <code>true</code> if it is read-only. Otherwise
	 *         <code>false</code>.
	 */
	abstract protected boolean isPropertyReadOnly( String propName );
	
	/**
	 * If property is shared by the group of elements, return the corresponding
	 * <code>GroupPropertyHandle</code>, otherwise, return <code>null</code>.
	 * 
	 * @param propName
	 *            name of the property needs to be handled.
	 * @return If the property is a common property among the elements, return
	 *         the corresponding <code>GroupPropertyHandle</code>; Otherwise
	 *         return <code>null</code>.
	 */