Central record re: files owned by the docs service account

[jennybc]

I don't think I can or should centralize the code to create the files owned by the docs account. But I need a central place to record how theses handled. I think vignettes/articles do already (or certainly can) hold their own setup/teardown code, probably in hidden chunks (that don't execute for every render).

A bigger challenge is that some examples would be better with pre-arranged files and I don't always want to inline the setup/teardown. Where to plan and record that?

[jennybc]

drive_reveal(), for example, could really use a more intentionally constructed set of files to work with, i.e. more like the ones used in the tests.

[jennybc]

This is partially addressed by 3c337dfc1c34b44ea8eb39b944349bd081f32b88, in which I introduce some official, persistent, world-readable example files. That helps, but doesn't fully resolve this dilemma.