Support for the property implementationType of executionListeners

[AlexanderSkrock]

The current version of the json schema support a new property implementationType for execution listeners which allows to make use of execution listeners other than scripts.

As additional idea, for convenience, if implemetationType equals class, then we could use the class which has the annotation if not explicitly configured with another value.

For reference, have a look here: propertes.json

If possible, I would like to contribute on this.

Kind regards
Alexander Skrock

[sascha-hanss-76]

If you have an idea how we can support execution listeners in generated templates, offer us a pull request.