So now inheritance works e.g. callbacks are called for subclasses

* Yes you read the diff right, I'm using class variables, I know
  I generally shouldn't but in this case they seem to pefectly
  fit my use case. E.g. they are visible for the whole class
  the alternative would have been to write some sort of lookup
  service - if you got another alternative or know why this
  would be better please tell me and send help :-)
added comment note