Add spec compliant ValidationErrors

[elbakerino]

The current internal error type need to get e.g. storeKeys, to be able to generate JSON-Schema spec. compliant error reporting in every position without unnecessary traversals.

This still must be compatible with the autowired store.

There should be two ValidityReporter in the future:

1. similiar to currently: saving the number of errors for the current level (instead of boolean like atm)
2. detailed: generating a JSON-Schema spec. compliant (and maybe a bit more) error data