Renderer tweaks

Changes from the glTF branch for consistency and to avoid conversions.

From CHANGES.md
* `PixelFormat`, `PrimitiveType`, `IndexDatatype`, `TextureWrap`, `TextureMinificationFilter`, and `TextureMagnificationFilter` properties are now JavaScript numbers, not `Enumeration` instances.
* Replaced `sizeInByte` properties on `IndexDatatype` with `IndexDatatype.getSizeInBytes`.

This also renames some uniform datatypes but no one will care outside of the renderer.