Converter for extruded solids with concave polygons

This MR adds the possibility to convert extruded solids that have concave polygons.

The side surfaces of the extruded are created by creating an outscribed, convex polygon and subtracting all the concave gaps. This is done in a recursive fashion, in case the concave gaps are themselves concave, until only a convex gap needs to be subtracted.

The required algorithm was adopted from ROOT here.

4 gdmls are added: one with extruded with one concave gap, one with two concave gaps, one with a simple nested structure, and a complex one with multiple levels.