Add API for building JavaFX scene graph for transient diagram views

[philip-alldredge]

It would be helpful to have an API that produces a JavaFX scene graph of a transient diagram-like view. This API would allow plugins to make use of the rendering and layout capabilities of the OSATE graphical editor.

The JavaFX nodes for the individual graphics are exposed but using those nodes requires the plugin developer to build the scene graph with those nodes. Visualizing an AADL model using those nodes would require significant effort and duplication of the capabilities of the graphical editor.

The components for building a scene graph and using ELK to layout that scene graph is internal. Add an API that will wrap those internal components into a basic API that can remain stable as changes are made to the API. Needed capabilities:

• Create a scene graph for a diagram-like visualization of model elements. API should allow specifying which elements are to be visualized.
• Allow applying styles to nodes
• Provide bi-directional mapping between the requested model elements and the scene graph nodes.
• Enable visualizing business objects which are not supported by the graphical editor by allowing specifying additional business object handlers.