counter: 1.3.0 - (RED) Introduced domain-class `User` as key

counter: 1.3.0 - (RED) Introduced domain-class `User` as key

* _GREEN:_ The `CounterApplicationIT` does _not_ reveal the bug!
* _RED:_ The `CounterStreamProcessorToplogyTest` fails with an exception,
  that gives a hint for the cause of the bug.
* The bug is caused by missing type-specifications for the operation
  ``cout()``.
* Before the introduction of the domain-class `User` everything worked as
  expected, because the class `Word` could be specified as default for
  the deserialization of the key.
** With the introduction of the domain-class `User` as key of the incoming
   messages, the default for the key has to switched to this class, to
   enable the application to deserialize incomming keys despite the missing
   type mapping.
** Beforehand, the default `Word` covered the missing type information
   for the ``count()``-operator.