Let `surface_factory.extrude()` and `revolve()` parse input SplineModel

[VikingScientist]

I think this is fairly straightforward. Given input an input SplineModel consisting of only connected curve pieces, construct an output SplineModel consisting of only connected surface pieces using the extrude and revolve for all pieces indiviually and independently.

Note: One thing to consider is that there is nothing preventing a (curve-)SplineModel to have only two connecting pieces at every vertex. A possible input is the following wire-frame