Update developer docs

* Add file upload API to developer docs
* Point setup instructions to the README
* Add instructions for combining/minifying static assets
* Update workflow overview architecture docs
* Update AI grading architecture docs
* Use napoleon keyword argument instead of kwargs
* Fix example usage docstrings in AI API

@stephensanchez Would you be able to add docs for the file upload setup?  Otherwise, I think everything else should be up-to-date.