FBXLoader: support morphtargets

[looeee]

Partial support for morph targets ( blend shapes ) in the FBXLoader.

Still to do:

• only morph positions is supported for now, no morph normals
• material.morphtargets = true needs to be set manually by the user
• animation is not supported (the user can manually set up animation of course, but animations in the loader will be ignored)
• remove code duplication between genGeo and genMorphGeo

[looeee]

Oops, I broke something when fixing conflicts. Don't merge yet!

[looeee]

OK, this should be good to go. I've split the monolithic genGeo function into genGeo, getGeoInfo, genBuffers, genFace.

Now genBuffers and genFace are reused when generating the morph target position attribute instead of duplicating the code.

[mrdoob]

Fixed a conflict. Should be good to go now?

[looeee]

Looks good!

[mrdoob]

Thanks!