Common: Re-add Deep Copy for Params

[holgerd77]

Just quickly dropping here so that it does not get forgotten, we need to re-add deep copy of the params in Common here #3545 (comment) and somewhere Jochem mentioned in one of these PRs (guess for the copy()-type method).

Otherwise this will have side effects in some cases.

(e.g. Common initialized with some param set, changing a param from the original param set for whatever reasons will change the param in Common if we do not deep-copy).

(might do this myself, just not in "dev mode" right now)