Scene related actions use "window" which is not part of class definitition

The `Action` classes defined here: https://github.com/enthought/mayavi/blob/master/tvtk/plugins/scene/ui/actions.py
have methods that reference `self.window`, but the classes do not explicitly have a `window` trait/attribute.

When they are instantiated, they are given a window, e.g.:
https://github.com/enthought/mayavi/blob/61ef7c0eebbdca474b7cfdf6082bfc17fb5aaf59/mayavi/plugins/envisage_engine.py#L85

It would be easier to understand if `window` was explicitly part of the class definition