Refactoring of adaptive cubic / support cubic:

1) Octree is built directly from the triangle mesh by checking
   overlap of a triangle with an octree cell. This shall produce
   a tighter octree with less dense cells.
2) The same method is used for both the adaptive / support cubic infill,
   where for the support cubic infill the non-overhang triangles are
   ignored.
The AABB tree is no more used.
3) Optimized extraction of continuous infill lines in O(1) instead of O(n^2)

src/libslic3r/Fill/FillBase.cpp

@@ -39,7 +39,7 @@ Fill* Fill::new_from_type(const InfillPattern type)
     case ipHilbertCurve:        return new FillHilbertCurve();
     case ipOctagramSpiral:      return new FillOctagramSpiral();
     case ipAdaptiveCubic:       return new FillAdaptive();
-    case ipSupportCubic:        return new FillSupportCubic();
+    case ipSupportCubic:        return new FillAdaptive();
     default: throw Slic3r::InvalidArgument("unknown type");
     }
 }