Proc-Mgr: workflow option modification faulty

[katharinabassler]

While updating the content of a workflow option seems to work correctly, deleting all options by means of specifying and empty workflow option list does not work. The workflow manager needs to be modified accordingly.

The same might be true for other collections contained in a Workflow, as well as for other services. It needs to be verified that overwriting values with null is indeed possible where it is allowed.

[emelchinger]

The behavior of updating lists is different as updating simple attibutes, describe it: #226