ENH: Added projection option to model slice display

Models consisting of thin structures (such as catheters, coils, stents), then are hardly visible in slice views, as their intersection with the slice is just a few points or small circles.

Projection option is already available for markups and annotations to show points in slice views that are out of the current plane and a common technique (maximum intensity projection) for images as well.

Now projection option is also added to model nodes. User interface is not yet added for this feature (it would require more experimentation to see how it is the best to expose this option), but can be activated from the Python console for a model node:

slicer.util.getNode('MyModel').GetDisplayNode().SetSliceProjectionModeToFull()