Rewrite Box2d Environments with PyMunk and PyGame

[jkterry1]

Right now, the box2d environments depend on pyglet for rendering, which doesn't allow for headless rendering and has created a host of miscellaneous issues if you search through our GitHub issues. Moreover, it depends on python bindings for Box2D that are no longer maintained and haven't been for 5 years (and after looking into it extensively getting them maintained is untenable). The only long term solution to using a maintained physics library is to use what most Python 2D game developers are now using, PyMunk (there's also basically no alternative). While numerous options exist for rendering, PyGame is suitable for our needs and is by far the best integrated with PyMunk of any options.

The replacement environments should:
-Merge different environment modes into a single code base for lunar lander and walker
-Retain identical reward structures
-Have as similar physics as the different engines allow
-Look as could to the old environments rendered as is reasonable.

We should also likely rename the environments to phys2d since this will require a version bump, but that's less important.

This issue is a consolidation of #2281 and #2347

[jkterry1]

Closing in favor of newer issues