Improve default and parameter docu for dispatcher.

The dispatcher will now run one pass
when called without any parameters, instead of using the number
of configured target wikis as a "magical" defgault.

Also improved help messages and logging.

Change-Id: I3745a1904c23786503e8e3b38c6a4c2a9ca3923b
Merge "Improve default and parameter docu for dispatcher."