dublicate triangles are only inserted once in the output mesh
adapted/re-enabled netgen triangular hull to tetrahedron mesh generation
added netgen algorithm
added netgen to algorithm factory and all.h, code cleanup
Merge branch 'FlorianRudolf/feature-netgen-make-mesh' into next
using netgen mesher to generate the volume mesh
using one viennamesh::netgen::mesh for multi-segment meshes (using ::netgen::FaceDescriptor for segment identification)
using one viennamesh::netgen::mesh for input and output
using one viennamesh::netgen::mesh as input and output
renamed viennamesh::netgen::output_mesh to viennamesh::netgen::mesh
Merge branch 'FlorianRudolf/feature-netgen-make-mesh' into next

Conflicts:
	examples/pipelines/oriented_hull.xml
Merge branch 'master' of github.com:viennamesh/viennamesh-dev
Added LIBVIENNAMESH compile flags to tetgen and vgmodeler compile flags