Two new features for BulbCalculator

Following a request from a BulbCalculator user, I started the work on implementing the export of the bulb into a STL model file, to be able to print a model with a 3D printer (or to be able to mill the bulb with a milling machine :-) ).

I also started to develop the possibility to add a hole for the keel, which is somewhat tricky since for any material you remove, you should update the bulb dimension to take care of the difference.

When I started to work on these two features, I realized thatI needed to do some preliminary works that have, as a result, optimized the code, especially the code that draw the 3D view of the model.

In the end I now have a more real wireframe view, while I added two other view modes: triangles and a real surface. The triangles view was a preliminary work to be able to create the STL file, the other one is just for fun ;-)