Moved materials/RenderTarget.js ⟶ renderer/WebGLRenderTarget.js

Refactored everything to use CamelCase naming for properties. Plus some smaller fixes here and there.

Went through all examples, all should work.

JSON files exported from Blender / converted from OBJ files still use underscored property names internally. I don't know, should these also be changed?

I don't remember when was the last time I used them. Current Web Developer Tools do this already for you.

Color::updateRGBA ⟶ Color::updateRGB

- getters/setters are no more in Vector3
  - object hierarchies thus don't use "isDirty"
  - this was completely killing performance for anything that was touching a lot of Vector3 like creation of meshes and dynamic buffers
  - even without this, performance of hierarchies went up (a lot)

- objects do not get passed renderer anymore
  - camera was almost also removed, but this is useful for LOD (though there may be some cleaner way to do this?)

- material ids are now unified, this makes "geometry.sortFacesByMaterial" faster (thus scene init / GUI blocking is shorter)

- all WebGL examples should work now (render-to-texture has weird lights and in some camera control feels different)

- CanvasRender still broken, despite many efforts :(
   - currently only points and lines work, faces don't show up. I think this may need assistance from mrdoob.

This is to be able to control depth buffer writing / testing on per geometry chunk level (before it was possible just to hack it on per scene level via exposed GL context).

Disabling depth test is useful for example for additively blended particles, handling of transparency or for having background textured quad.

Another option would be to have it on per object level, but then this could prevent different handling of objects with both transparent and opaque parts.

Also in this commit:

- more progress towards mesh vertex colors
- less matrix multiplications in render call
- fixed ugly bug in doubleSided / flipSided handling
- cleanup of materials
    - added a lot of missing stuff in debug strings and parameters handlers
    - normal and depth materials now have opacity parameter
    - wrote comments for non-obvious things

Moved near/far values from MeshDepthMaterial to Camera (CanvasRenderer/WebGLRenderer/WebGLRenderer2).

Cleaned up shader snippets in WebGLRenderer2.

Depth material finally works also in ANGLE.

Implemented material blendings (THREE.NormalBlending, THREE.AdditiveBlending, THREE.SubtractiveBlending) in CanvasRenderer
Added MeshNormalMaterial (per face)

Cleaned up CanvasRenderer and SVGRenderer code a bit.