This commit changes OBJExporter so it handles BufferGeometry directly.

Bugfix: The binary STL exporter didn't handle meshes imported from binary STL files (BufferGeometry)

* When an object child is a THREE.Line parse and output to obj file.

* Handles separate cases of type Line and type LineSegment.

* When an object child is a THREE.Line parse and output to obj file.

* Handles separate cases of type Line and type LineSegment

remove nbVertex; it is not needed

Before, only the vertex value was altered to reflect the 1-indexed nature of OBJs. This fixes uvs and normal values as well.

I applied normal matrix to exported normals, deleted dummy texture coordinate writing, and an unneccessary line. I also made some modifications in the example.