Support the rendering of lines

[kovacsv]

Some formats can contain independent lines.

• line threshold calculation
• obj import
• obj export
• gltf import
• gltf export
• 3dm import
• 3dm export
• stp import
• fbx import

[heningyuan6256]

I have noticed that in your project https://github.com/kovacsv/occt-import-js, there is an example that has already implemented rendering of lines. I believe it shouldn't be too difficult to port it to the online3DViewer.