Bug 169025 Supports overridden on editor contribution
After contributting a new editor to the multiPageReportEditor, supports to enable the new editor to override a editor by assigning the ID.
UI/org.eclipse.birt.report.designer.ui.editors/src/org/eclipse/birt/report/designer/internal/ui/extension/FormPageDef.java
return false;
	}
	private Object loadClass( IConfigurationElement element,
			String attributeName )
	{
		Object clazz = null;
		try
		{
			if ( element.getAttribute( attributeName ) != null )
			{
				clazz = element.createExecutableExtension( attributeName );
			}
		}
		catch ( CoreException e )
		{
			ExceptionHandler.handle( e );
		}
		return clazz;
	}
	public IReportEditorPage createPage( )
	{
		Object def = loadClass( element, ATTRIBUTE_CLASS );
		if ( def instanceof IReportEditorPage )
		{
			return (IReportEditorPage) def;
		}
		return null;
	}
}