NRRD format integration to MeshFactory

[enicolasgomez]

Goal is, similar as we've previously done with already supported formats (OBJ, GLTF, etc) we should add a loader for the mentioned format:

geppetto-meta/geppetto.js/geppetto-ui/src/3d-canvas/threeDEngine/MeshFactory.js

Line 54 in b40447e

this.loaders = {

There's already an isolated viewer in here.

#417

One of the known challenges of this format is that the volume box is defined on the specification header:
https://teem.sourceforge.net/nrrd/format.html

So we've previously encountered issues when using the ThreeJS Canvas instance we are running on geppetto-meta, as the following items seem to be defined on the header:

• 3d axis do not have a constant magnitude scale
• orientation of the 3d axis is also pre-defined
• there's potentially some camera state tweaking needed because of this

This card closes #417 as this is the actual integration to the code base.

[enicolasgomez]

On a side note, as performance will be a challenge, consider https://github.com/google/neuroglancer