QAbstractCameraController - escape key should not trigger "view all"

This commit:

https://codereview.qt-project.org/#/c/226879/

changed the abstract base class for camera controllers to hard-code the escape key to trigger a "view all" of the scene.

For most applications, the escape key means "undo" or "cancel", so this is very counter-intuitive. This is really an app-specific functionality and does not belong in this base class. In addition, there's no clean way to remove this functionality.

I would recommend either reverting this change or providing a way to cleanly turn off this functionality.