This also reduces number of VBOs. There aren't many of them anyways, but it's always nice to have less ;)

It did seem to help quite a bit ;)

replacing with `this`

A lot of things going on in this commit:

- added tangents computation for geometries
    - mesh must have UV coordinates
    - to be called explicitly once geometry is loaded like this: geometry.computeTangents()
    - tangents are stored in Vertex objects
    - quads are not solved properly (though workaround hack seems to work at least somehow, as far as each vertex appears at least somewhere)

- extended VBOs in WebGLRenderer to include tangent streams (when available)

- added "normal" shader to ShaderUtils (to be used with MeshShaderMaterial)
   - Blinn-Phong with one directional and one point light (7 varyings gone, just one spare)
   - normal maps are in tangent space
   - displacement maps use simple luminance value (could be changed if better precision is needed)

- displacement mapping uses vertex texture fetch
    - this requires GPU with Shader Model 3.0
    - not currently supported in ANGLE
    - for this, added "supportsVertexTextures" method to WebGLRenderer API, so that application can handle this

`THREE.Matrix4()` → `THREE.Matrix4(  n11, n12, n13, n14, n21, n22, n23, n24, n31, n32, n33, n34, n41, n42, n43, n44 )`

Added vec3 and color parameters for MeshShaderMaterial. Also moved normal and view matrices into default parameters.

Firefox doesn't like Typed Array constructors without explicit sizes.

Also in Firefox there were some weird artefacts in Perlin noise when using Int8Array (patterns were repeated across diagonal lines).

For this extended Cube primitive with "sides" parameter.

You can use it to switch off cube faces like this:

    var cube = new Cube( 100, 100, 100, 1, 1, materials, false, { ny: false } );

Default is all six faces on => { px: true, nx: true, py: true, ny: true, pz: true, nz: true }

Thanks again Firefox for verbose WebGL warnings.

Also made code slightly faster (and more Pythonic).

Pushed revision number to 31.