Task Transitioncontroller: update check's for multiclient wizards.

The wizard for `multiclients` tasks are now only necessary when the tasks concerns multiple
AdminUnits. Tasks concerning only multiple OrgUnits don't need a wizard and successor predecessor copies.

@deiferni please take a look.
@phgross i would rename this method to `_is_responsible_org_unit_part_of_current_admin_unit`, this explains the `type of unit` of the first `unit`.