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
abstract public GroupPropertyHandle getPropertyHandle( String propName );
	
	/**
	 * If the given property is a common property, value will be returned as a
	 * string if all values within the group of elements are equal. If the
	 * property is not a common property, return <code>null</code>.
	 * 
	 * @param propName
	 *            name of the property.
	 * @return the value as a string if the property is a common property and
	 *         all the elements have the same value. Return null if the property
	 *         is not a common property or elements have different values for
	 *         this property.
	 * @see GroupPropertyHandle#getStringValue()
	 */
	public final String getStringProperty( String propName )
	{
		GroupPropertyHandle propHandle = getPropertyHandle( propName );
		if ( propHandle == null )
			return null;
		return propHandle.getStringValue( );
	}
	/**
	 * Indicates whether the group of element share the same value for this
	 * property.
	 * <p>
	 * If all element has a <code>null</code> value for this property, it is
	 * considered that they share the same value.
	 * 
	 * @param propName