Corrected docs of accept in aggregate

The JavaDocs which were still mentioning registering were corrected to
mention accepting.
Removed debug statement
Removed unused status type from Core API

The ChargingStationRegistrationStatus type was initially used to
directly communicate results back to the caller when the OCPP addon did
not have a view model yet. As the OCPP addon now has a view model and
doesn't use this return value it has been removed to keep the Core API
to a minimum.