Texture improvements and fixes.

- move TextureType enum into separate file.
- AbstractRenderingStreamer::loadTexture(...) returns a reference and gets texture type and layer parameters.
- Serialization::loadTexture(...) returns a reference and gets texture type and layer parameters.
- Texture:
  - Check number of layers in constructor;
  - fix several errors regarding cube map textures.
- TextureUtils:
  - extend createTextureFromBitmap(...) to create textures of different types;
  - remove createCubeTextureFromBitmap(...)
  -  fix createHDRCubeTexture
- adaptations.