Create a fault-barrier for all timer-tasks

Errors reported for the IntegrityService has shown, that the workflow just terminates without a warning, if one of the steps throws an exception.
A fault barrier for the workflows within a scheduler is therefore needed (the scheduler for the workflow is in the 'service' module).

See the discussion at 'https://sbforge.org/fisheye/cru/CR-BITMAG-210'.