Polygons don't change when in layer-view. There's already an analogous elementCount property anyway, so a vertexCount property can't do much harm. Just keep in mind that when the polygons are altered, it should be either done via build, or the lineMeshXXXCount methods should be used instead.
Instead of re-uploading the mesh each time the range changes, handle the range in the shaders with the new draw-range parameters. This does however, mean the range has to be in vertices, not in elements. This necessitates some changes to the simulation-view, and some added bits deeper in the base code. Mainly, since each time the type of a line changes, there is an extra vertex, there needs to be a type-change count available to get from 'paths' to range indices.
Changed to "is None" insted of "== None" to test if numpy.array was initialized
Added extruder to PathSegment in Cura.proto
Changed index_pattern to class variable in Layer.py
