JSON is order preserving, but should be strictly ordered

[sveinse]

The json file order is not stable enough. E.g. by following the procedure:

1. Convert OD -> JSON
2. Edit OD file with odg edit
3. Convert OD -> JSON
4. Compare files (e.g. in PRs) reveal two very different ordered files

This is because the OD file is not stable and thus the JSON files are different. JSON are order preserving.