Merge branch 'triangulate_copy_properties' into 'master'

Copy per-halfedge and per-face properties to new elments during triangulation

This is an attempt to fix an issue we encountered when loading a textured quad mesh and triangulating it:
In the triangulated version, the respective values of the per-halfedge texcoords and face texture index properties  were not assigned to the new triangles that were created during triangulation.

See merge request !57
6 jobs for master
Status Name Job ID Coverage
  Test
passed clang-c++11 #4665
Linux

00:20:52

passed clang-c++98 #4667
Linux

00:14:38

passed gcc-c++11 #4664
Linux

00:05:00

passed gcc-c++98 #4666
Linux

00:04:19

passed macos-c++11 #4668
Apple

00:16:09

passed macos-c++98 #4669
Apple

00:14:12