[api] Modeling different types of interventions

[adam2392]

Not all interventions are equivalent. There are different kinds:

• do(X=x) = set the value of X to a scalar
• do(X=f(.)) = set the value of X to a deterministic function that we can evaluate
• "mechanism change" = alter the functional relationships of one or all the parental relationships wrt the node
• "additive" = add noise

Mechanism change can be further decomposed to:

• alter the structure (i.e. SCM arguments)
• do not alter the structure (parents are exactly the same)