[JavaFX] Add a constructor in the base class for single controller views.
Current situation.
The AF3FXViewPart class only allows to create views that carry a FXML layout file, which defines the views layout. However, there are multiple cases where only a single controller is required. The additional layout files are boilerplate in these cases.
Resolution.
Modify the constructor setup to be more flexible such that AF3FXViewParts can be created without providing a FXML layout.
(from redmine: issue id 3463, created on 2018-06-28, closed on 2019-09-30)