atari-py ROM configuration

[rossbar]

The latest atari-py wheels break the pong tutorial with an exception about needing to install/configure appropriate ROMS. This is a known issue: open-ai/atari-py#79. Proposed workaround is to use an older version of atari-py==0.2.5 as suggested here, but this requires local building of the wheels, which is at the core of #69.

In the long run, it would be great if we could switch to using the newer atari-py wheels and figure out the minimal ROM configuration to get the example working sustainably again.

[Mukulikaa]

Since atari-py has been deprecated, we'll have to switch to Arcade Learning Environment. I think we'll have to import the ROM separately; it won't be available through ale-py.

[melissawm]

I did some reading on this and it doesn't seem so trivial, so for now I'm proposing just pinning gym==0.19 (which fixes CI) and leaving this issue open so we can fix this properly in the future.

[melissawm]

Once we fix this, we can enable windows-based CI workflows - see #127