Petting Zoo environment for LBF

[efosong]

I wrote a PettingZoo implementation of LBF. Perhaps one day we could get it featured on the PettingZoo website, which would be good for visibility.

This might be a bit of an annoying change though since:

• I left the gym env in, but moved it
• The interface for the PettingZoo version is quite different (e.g.: ids like Foragaing-8x8-3p-2f-v2 are not used, in preference for just lbforaging_v2 and leave it up to users to specify the environment and report environment parameters in their works)
• The PettingZoo implementation is pretty much separate from the gym implementation such that changes to one won't automatically appear in the other
• The predefined agents probably don't work with the PettingZoo env
• I factored Player out of the code
• I haven't fully tested grid obs, but I'm about 60% sure it works correctly

Even if you don't want to merge this (really, I made it for my own use), I wanted to start a conversation about a PettingZoo implementation (perhaps wrapping the gym environment more directly?). Or maybe you do want to merge it, but in some different way.