first attempt at using BufferGeometry.

seems quite a bit faster, possibly even more so if we'd use indexing,
but i'm not sure if that would make any difference or is just used for
custom attributes/data.
use controls from three.js.
actually use buffer geometry.
don't compute the bounding sphere.

seems to improve performance and i don't quite know what it's used for
anyway.
support basic (e.g. correct colors) lighting again.

still it's a bit weird as the trixls only seem to get lit from the front
and the back.
generate a few cubes on startup.