allow SaQC eat itself

followup of #128 (closed)

may we should allow __init__ to handle other saqc instances and since !357 (merged) we allow lists of objects so we could finally implement something like a merge

changed milestone to %2.3.0

added needs discussion label

mentioned in issue #128 (closed)

added feature label

removed needs discussion label

added accepted label

added category: public API category: register/core usability labels

changed milestone to %Someday