♻ replace env with cache

[hgwood]

Currently the code in env.js loads a bunch of stuff from the .petibrugnon directory and makes it available to all other code files. The env.js code makes assumption about the state of the file system and the rest of the code files make assumptions about what they'll find in what they import from env.js, which might be wrong. All of this makes the program brittle. Note that most of what can change in env is stuff downloaded from the CodeJam API.

I should replace the env mechanism by caching. The program should simply fetch what it needs from the CodeJam API and cache it in local files. Only paths should come from env. I should use the same technique used for credentials (see here), but with different cache rules.