Eradicated admesh from TriangleMesh:

TriangleMesh newly only holds indexed_triangle_set and
TriangleMeshStats. TriangleMeshStats contains an excerpt of stl_stats.
TriangleMeshStats are updated when initializing with indexed_triangle_set.

Admesh triangle mesh fixing is newly only used when loading an STL.
AMF / 3MF / OBJ file formats are already indexed triangle sets, thus
they are no more converted to admesh stl_file format, nor fixed
through admesh repair machinery. When importing AMF / 3MF / OBJ files,
volume is calculated and if negative, all faces are flipped. Also
a bounding box and number of open edges is calculated.

Implemented its_number_of_patches(), its_num_open_edges()
Optimized its_split(), its_is_splittable() using a visitor pattern.

Reworked QHull integration into TriangleMesh:
    1) Face normals were not right.
    2) Indexed triangle set is newly emitted instead of duplicating
       vertices for each face.

Fixed cut_mesh(): Orient the triangulated faces correctly.

sandboxes/aabb-evaluation/aabb-evaluation.cpp

@@ -212,8 +212,7 @@ int main(const int argc, const char *argv[])
         return -1;
     }
 
-    mesh.repair();
-    if (mesh.facets_count() == 0) {
+    if (mesh.empty()) {
         std::cerr << "Error loading " << argv[1] << " . It is empty." << std::endl;
         return -1;
     }