Develop a schema for scraper output

[shaperilio]

We have schema definitions for scrapers, but now what they output. We should enforce things like administrative levels and measured quantities (e.g. cases, deaths, etc.).

Along with this, I propose we write a scraper skeleton, with a list of data requirements and pseudo-code (or a code template of some sort) showing what needs to be done and when.

Schema should be validated in yarn test.

@jzohrab @shaperilio