Quantizedmesh vertex normals

Going public with current implementation of quantized-mesh per vertex normals.  This is a work in progress; will be improving doc, adding unit tests, and reverting changes to CesiumViewer.
1. Consistency is important in its own rite.  We use `!==` everywhere else we call `indexOf` and should do the same here.
2. When the code is compiled and optimized by the browser, it's possible that `>` and `!==` do not have the same performance characteristics (though they probably do), so using `!==` is more exact for what we want.

I also just noticed you are using `"` instead of `'`, one of our other style guidelines is to always use single quotes (except in the `"use strict" case, and we're considering changing that as well).