[Development] QSettings refactor updates

[Branislav Katreniak]

> Cache format: binary json

You use json internally as cache. What is the motivation to introduce
new classes with similar API like QJson classes?

Is the implicit shared semantics not suitable for this use case? Can
it be addressed in QJson classes directly?

If Qt gets some type safe wrappers above the QConfig string based api,
it would be great to have these wrappers above QJson classes directly.

Kind regards
 Brano