missing attributes in latest release

```

 File "src/layout_server/__init__.py", line 29, in init layout_server
         cursor_keys = [lay.KeyCode.Left, lay.KeyCode.Up, lay.KeyCode.Right, lay.KeyCode.Down]
     AttributeError: module 'klayout.lay' has no attribute 'KeyCode'

```

it seems the KeyCode and ButtonState enums are not available as attributes of the lay module in the current version of Klayout


@sebastian-goeldi 