Large terrain 94

Contains everything mentioned in #94:
- larger landscape (looks quite realistic =) )
- navigation limited to the terrain extents (- view distance)
- terrain blended to the sky color at the horizon (we really need a skybox!)

Also includes smaller performance improvements, but we have to check that again after #86 (current implementation with getPixel is expensive..), that's why i would remove the interaction performance counters for now