Mine Up optimized 0.2.5

Version 0.2.5, Experiment with the performance
Changes:
Fixed: User can't choose one world in two places.
Added: Increased perfomance of the renderer and chunks loader.

Now you can enjoy the view of skylands from the ground and vice versa. Earlier it was not possible because the view was limited with 48 blocks (up and down). Now it depends on graphics settings.
And I also changed a bit the shape of viewport, so all these changes led to a better performance.