Fetch all child pcc set objects by default

[arthur00]

Example: UberCar inherits from Car. When fetching Car, all Car's children should also be fetched by default. This can be done client side (e.g. Getter(Car) == Getter(Car, UberCar)) or server-side. Client-side seems to be less disruptive.

[arthur00]

This is not working yet. @lordnahor is working on a fix.