[Python Core] Keyword for direct passthrough of **kwargs to super().__init__

[miallo]

Since it would probably be quite bad to just turn this feature on by default for all classes I thought I would invent a keyword that (if present in the init) would do it. If not: do it the 'old' way. What you might see from my example code is that the super().__init__ calls don't have the ***pass_through_kwargs specified.