Eventually switch from Matrix4 to the web-standard DOMMatrix.

[trusktr]

LUME 3D elements originally used DOMMatrix (that I polyfilled) before switching to Three.js. Now, we'll convert lume/glas to using DOMMatrix, and eliminate the transform conversion hacks we have in the main lume lib (currently converting from from CSS left-handedness and Y down to Three.js right-handedness Y up, which adds a layer of indirection that would be awesome to eliminate).