This reverts commit f3f93232.

GLTFExporter: Check isInterpolantFactoryMethodGLTFCubicSpline property of factory method to detect cubic spline interpolant

As described in gltf specification, (UNSIGNED_INT) is 4 bytes. 
This commit solve the fact that the exporter failed to export correctly assets containing faces with vertexe's indexes above than 255.

This change ensures the allocated buffer size is aligned to the next 4-byte boundary. See https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#data-alignment 

There may also be other allocated buffers (glb output?) that require 4-byte alignment, but this fixes validation of the exported file for me. 

This change is cribbed from getBufferPadded.js of obj2gltf but is modified for this use case.

Update padding

If an object name is a number it is currently copied to the gltfNode as a number. This results in gltf validator errors:

 "code": "TYPE_MISMATCH",
                "message": "Type mismatch. Property value 26 is not a 'string'.",
                "severity": 0,
                "pointer": "/nodes/1/name"

This change ensures gltfNode.name is a string in all cases.

Fix GLTFExporter processAnimation(), KeyframeTrack does not have interpolation then we need to use .getInterpolation()