Optimizing GL Buffer Usage

[vojtatom]

Several optimizations:

• store colors as Uint8Array and normalize to floats,
• same as above for ids,
• precompute dot product of normals and single directional light and pass the result as dot to shaders where applicable,
• optimize assemblers to assemble metadata and id buffers only when explicitly requested.

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As of b907925:

• 785 MB of resources downloaded
• memory utilized by three.js: reduced from 1475 MB to 732 MB.