FBO: All attach... methods support texture level and layer.
Fix debug output.
Minor Texture redesign.

Serialization and TextureUtils:
- Remove mipmap and clamping options from loading and creation functions.
Texture:
- Add additional texture type value (independent from OpenGL-Constants)
- Replace filter enums by OpenGL-independent (and more robust) booleans.
- Add planMipmapCreation(...) and several getters
- Remove glu-mipmap fallback