ColladaExporter: Optimize material export and added example

[clintonman]

ColladaExporter material bugs:
was using groups to determine material count, in my tests the group count was always zero resulting in no material export
changed to take the largest value between the group and material counts

removed incompatible tags on collada shaders - https://www.khronos.org/files/collada_spec_1_4.pdf
constant shader does not have diffuse, shininess or specular tags
lambert shader does not have shininess or specular tags

added web page to demo the changes

[WestLangley]

<title>three.js webgl - collada exporter</title>

and probably rename file to misc_exporter_collada.html

[clintonman]

I made the 2 changes above and just noticed the files.js
Should I add this to the "misc" section of the list?

[Mugen87]

Yes, otherwise the example won't be visible on the overview page: https://threejs.org/examples/

[Mugen87]

For testing: https://raw.githack.com/clintonman/three.js/colladaexport/examples/misc_exporter_collada.html

[Mugen87]

/cc @gkjohnson

[gkjohnson]

This looks good to me -- my only comment is that it seems like the constant shader type apparently doesn't actually map very well to the MeshBasicMaterial, but it doesn't seem that there's a much better option in the spec. Maybe it's worth adding a console warning like in the GLTFExporter stating that the material textures aren't going to be exported as expected?

[Mugen87]

Maybe it's worth adding a console warning like in the GLTFExporter stating that the material textures aren't going to be exported as expected?

I think this can still be done in a separate PR.

[mrdoob]

Thanks!