Blender Git Loki

Export triangulated mesh, not modifying the scene

Add UI checkbox for triangulating before writing the OBJ file.
The scene is not modified at all. Actual modifier should be used if one
needs the mesh to be modified too.

The settings for triangulation are the same as default ones of the
modifier:
ngon-method: "Beauty", quad-method: "Shortest Diagonal", min vertices:4