JavaFX: Add Single-Node View support.
- Modify the constructors such that AF3FXViewParts can be created that only contain a single FX node/control, and do not come along with a FXML layout file.
- Due to signature conflicts, the css location must be given in the constructor. The default case is to use "null" such that the OS-native look is used.
- Add a method "setChildNodeFinal" that must be used to add the FX node to the view. It is not possible to do this in constructors since the FX toolkit is not initialized at this point in time.
Issue-Ref: 3463 Issue-Url: https://af3-developer.fortiss.org/issues/3463 Signed-off-by: Alexander Diewald diewald@fortiss.org