(build) Dont Crunch the data/ Folder

[sabine]

In response to #1987, I realized that we shouldn't be crunching the data/ folder with ocaml-crunch.

Here is a patch that changes ood-gen to use bos to read the markdown and YAML files directly from the file system.

On my machine:

before:

real    0m21.262s
user    0m57.290s
sys     0m13.810s

after:

real    0m12.898s
user    0m42.419s
sys     0m10.785s

This patch changes nothing about how the media files or static assets are crunched and served.