Moving away from multi-subregister model

[strogonoff]

In the next version of ISO 19135 implementation in RegistryKit, it was decided that subregisters will have to go away. I assume we will have to restructure and rephrase the registers page to not use the “register” terminology when referring to languages. Is there anything preventing us from doing it? How do we handle multiple per-language managing organizations/control bodies, will we have to present all that information as freeform text in the unified register content summary?

cc @ronaldtse (and should we ask Mike for input?)