Refactoring: distinguish content- and formatting-related messages

Goal

JSON reports have to have all the messages which we consider as “content messages”.

Formatting related messages (such as that one about the limit of lines in tables) should not be present in JSON, they live only in markdown reports.

TODO / How to implement

@dmius —- provide details

Acceptance criteria

Check JSON reports. Compare them with markdown reports. Ensure that JSON reports:

• contain all non-formatting messages used in markdown reports,
• do NOT contain any formatting messages.