Add anisotropy property to renderer and material for configuring it globally and per material respectively

[mrxz]

Description:
When viewing textures under a steep angle it can quickly become "blurry" and "greyish". In those cases anisotropic filtering can make a huge difference in visual quality. See for example the effect it has on the aframe-environment-component: supermedium/aframe-environment-component#95

Meta sets this on all textures for loaded models in their Project Flowerbed and in a blog post they summarize it as:

On your environment textures: Turn on anisotropic filtering

Three.js provides two ways to configure this, one setting a global default and the other on a per-texture basis. This PR exposes both of them; on the renderer system and material component respectively. For the material it will apply to all texture maps for that material, but in practice you'd want them in sync anyway. The code doesn't have to worry about unsupported values or invalid combinations as Three.js handles that already :-)

Changes proposed:

• Add an anisotropy property on the renderer system for setting THREE.Texture.DEFAULT_ANISOTROPY
• Add an anisotropy property on the material component

[dmarcos]

Thank you so much!