Produce self-contained schemata in a single JSON file

[saraedum]

Quite a few tools are not so happy about the $ref pointing to external files. Having each schema self-contained in a single file would make things much easier to use.

Of course, we do not want to actually edit such huge schemata but we should provide a distribution of the schemata as self-contained json files. E.g., we could make this a pip-installable package that ships these combined files. Something like https://github.com/gazpachoking/jsonref could help with that.