Update triangulation algorithm

[lilleyse]

Fixes https://github.com/AnalyticalGraphicsInc/obj2gltf/issues/147 by updating to the latest triangulation code used in Cesium. This fixes a model that wasn't triangulating correctly in master. This fix required updating Cesium so I updated other dependencies with it.

csxirc5h.i2b.obj

Before and after:

There are still some back facing polygons but I confirmed they are present in the original model too. We don't yet do that sort of correction.

(Backfacing polygons on the steps)

I checked that the new method still triangulates these models correctly:

https://github.com/AnalyticalGraphicsInc/obj2gltf/issues/33 https://github.com/AnalyticalGraphicsInc/obj2gltf/issues/50 https://github.com/AnalyticalGraphicsInc/obj2gltf/issues/79

One thing I'm not completely sure about is whether PolygonPipeline.computeWindingOrder2D is enough to check the winding order. Would it need to use the normal like the 3-sided case?

[lilleyse]

@hpinkos could you check this out? The new code starts here: https://github.com/AnalyticalGraphicsInc/obj2gltf/pull/157/files#diff-608b0b654865416bb99fb5d336cf3307R297

[hpinkos]

I don't have write access to this repo so I can't merge it, but this looks good to me @lilleyse

[lilleyse]

Thanks @hpinkos. I'm going to go ahead and merge.