Introduce a "strict" mode for the json format

[matejcik]

In order to place less requirements (and less features) on the consuming implementations, there should be a "strict" variant of the JSON information, defined basically by "whatever can be preprocessed has been preprocessed".

As a rough draft, this would mean:

• no includes, all required files are inlined
• no relative paths
• all display.definitions are inlined

Generally all fields that can contain "either one format or another format" should pick one for the "strict" version, to which the other options can be converted.

Given such spec, we can build a preprocessor that converts the "full" format into the "strict" format. That way it is possible to store the "full" reader- and author-friendly files in a central repository, but can easily preprocess them, with a common preprocessor implementation, into the "strict" machine-friendly versions intended for consumption by wallet software (or other steps of a pipeline, such as conversion to a binary format for a HW wallet)