Hardening conversions of old definitions to new framework

Within this ticket a lot of ad-hoc found issues with conversions were fixed. Mostly what was found within DEV-1413.

Original old description

EDIT: converted field is working properly, only this label is broken via converter. In fact converter should handle these cases by disabling field unless default SwitchableTransformer or CookieFieldTransformer are used.

In the attached image the label informs us about non-converted field.

Can be found in a Choose Audience dialog triggered on a page variant in the new pages app.