Add the environment variable KYSYS3DMOD to define a default path for 3D models.
Add the environment variable KYSYS3DMOD to define a default path for 3D models.
If it is not defined by user, it is set to a legacy 3D files path.
The default value needs to be fixed on MACOSX.
This change could be better, but it is compatible with environment variables and the old way ( defined search paths) to find 3D shape files.
3D shapes files names can  also include an environment variable definition, like libraries names.
However using KYSYS3DMOD in these names is not required.
If the 3D filename is a legacy name, KYSYS3DMOD is automatically used as default path.