* Move fx-base classes dealing with controllers to a dedicated package
  to prepare adding more base classes.
* Place type checks in the constructors of AF3 base classes to avoid
  them in the large set of concrete classes.
* Transform several base classes to classes such that they can be
  directly instantiated by factories if no specialization is needed.

Issue-Ref: 3883
Issue-Url: https://af3-developer.fortiss.org/issues/3883


Signed-off-by: Alexander Diewald <diewald@fortiss.org>