adds an onStart event to the loading manager
i tried to "mrdoob style" as i went along

Fixes #5570

centroid was originally used by CanvasRenderer, now that it computes it as needed we don't need the bloat anymore.

@antoniovazquezblanco could you check that I didn't broke anything?

See #2628 and #2623

I tried to move BinaryLoader to /examples/js but SceneLoader needs it.
Curious to hear what people thinks about this change.

(Phewww!) I'm sure there are still things I missed...

It was quite a pain - ArrayBuffers / Typed Arrays are fussy about byte alignment - but seems to be worth it.

Parsing times are down (modest gains for small objects / Firefox, bigger gains for large objects / Chrome, performance gains from 10% - 200%).

Also as a positive side effect, changing interleaved face arrays into uniform arrays seems to have helped a bit with gzip compression (about 6% smaller size for gzipped 526K Lucy).

Work-in-progress => do not merge yet.

OBJ converter, JSONLoader, BinaryLoader and some examples are done. Still need to do Blender exporter, SceneLoader and more examples.

Advantages:

- faster parse times
- bypass array initializer size limit in Firefox
- no more crashes in Chrome 15 (caused by too many concurrently active workers)

Disadvantages:

- more browser UI freezing
- multiple models tend to appear all at once with the last one (instead of popping up progressively)

Do not use for anything, this is just snapshot of a test in progress. I solved quite a few issues, but many things are still clumsy and broken.

Also updated corresponding examples.

Also tried to clean whitespace for ColladaLoader. This thing is so massive.

extras/collada/dae.js > extras/loaders/ColladaLoader.js

removed LoaderOld.js