Renderer: Experiment with Mipmap textures

[Helco]

To improve texture mapping quality when textures are shrinked we should see if mipmapping improves the quality enough to justify the upto 33% more memory usage, also:

• Can the mipmap textures be generated on level-load?
  • Linear/Bilinear/Trilinear filter?
  • On-the-fly dithering?
• Is blending between mipmap levels necessary?
• Should there be an abstract Sampler interface (with compile-time implementation)?