Make everything buildable again

Went through all files and fixed all type errors.  Most things seemed like
defaults, inserted TODOs with my name when I was unsure about what I was
adding.

Main change was deleting definitions from python-lib.rkt in exchange for
python-lib-bindings.rt; I would love a review of that to see if I broke
anything.

Tests currently return an error that LexExceptAs reached desugaring when it
should not have; that is the next thing to triage.