Remove AtariEnv in favour of official ALE Python package

[JesseFarebro]

This PR removes atari-py in favour of the official ALE package ale-py. More information can be found in Farama-Foundation/Arcade-Learning-Environment#382.

The major changes to Gym will be as follows:

• ROMs are no longer packaged as part of atari-py. The current solution is to use python -m atari_py.import_roms. The new ale-py method of importing ROMs will be the shell command ale-import-roms.

• clone_state(), clone_full_state() will return the actual ALEState object now instead of an object meant for serialization. This should have no impact on users as ALEState can be Pickled and serialized without issues.

• It is now recommended to use gym.make('AtariID', render_mode='human') instead of env.render(mode='human') for both render modes. ale-py shipps now with SDL2 and supports full 60FPS viewing, audio, scaling, etc. You don't get this by using env.render()

• Environment defaults have changed: frameskip = 5, repeat_action_probability = 0.25, full_action_space = True. This follows the most recent methodology set out in Machado et al. 2018. This has no impact on the existing Gym IDs which remain unchanged.

It's worth noting that as far as users are concerned everything is backwards compatible. ale-py will still search for ROMs that were imported via atari-py and the environment parameters for v0 and v4 haven't been changed.

[jkterry1]

@JesseFarebro I believe the version of ALE-Py needs to be pegged instead of just specifying a minimum version since this impacts environment logic?

[jkterry1]

For additional context, the problem with Atari-Py is that it used an incredibly out of date version of the ALE with many now fixed inconsistencies, bugs and performance issues. This has been a planned upgrade to Gym for something like 2 years now.

[JesseFarebro]

ALGymEnv still accepts image as an obs_type but will display a deprecation warning asking the user to switch to one of: rgb or grayscale.

[jkterry1]

@JesseFarebro you said that opencv would be removed from all the Atari environments, but it's still living there (at least in setup.py for [atari])

[JesseFarebro]

@jkterry1 so I was mistaken where OpenCV was used. It's used in the AtariPreprocessing wrapper to do image resizing. This wrapper won't be changing for the time being. Eventually, we'll be able to remove the wrapper and dependency on OpenCV but that's down the road.