Standardize the MeshLineMaterial, support fog and logarithmicDepthBuffer.

[Jeremboo]

This is a MINOR update !

I rewrote the structure of the MeshLineMaterial to standardize it closer to the others Three.Js materials but in avoid any breaking changes.
I confirm that did not change any props or the current shaders core too.
I just took advantage of this rewrote to add the support of the fog and the logarithmicDepthBuffer.

Details:

• I directly made it herited to a ShaderMaterial instead of a Material who returning a RawShaderMaterial. That allow to have the material properties dynamic and fix some user's issues who use them directly (MeshLineMaterial() quietly modifies the parameters object passed to it #70, Keep MeshLineMaterial from modifying parameters passed to it #71, Update color dynamically possible of MeshLine? #67).

• I updated the RawShaderMaterial to a ShaderMaterial to be more generic and enable the usage of the WebGLProgram. The material can now detect automatically some rendering parameters.

• I included the logdepthbuf_pars & fog_pars to fix Depth Issue #65, Effected by fog #48 and Support for the current fog shaders in THREE #32 thank to the previous point. It should be easier to also include other supports like the tonemapping_pars.

[spite]

Merged, thank you very much!