[feature] Object>>childResponsibility

[ngarbezza]

Is your feature request related to a problem? Please describe.
We want to give explicit support for abstract methods and have an error when this code is reached. We won't use subclass responsibility because we could use it on classes or objects in the same way.

Describe the solution you'd like
any object should understand childResponsibility which will raise an exception if it is called (preferably with an error message like "this object had the responsibility to implement #xxx").

[ngarbezza]

added in 48d8d8f