Some bug fixes and cleanup.

Bugs fixed:
1) Chunks with no blocks in render pass 1 (but with blocks in render pass 2) not being drawn. (e.g. chunk with water and air, you can see it in the top middle part of the screenshot below)
2) Border chunks not being drawn in levels which have axes that are not multiples of 16.
3) Progress bar being completely white.
4) Screenshots being rather stuffed up. (as in the screenshot below)

Also, some general cleanup was done in LevelRenderer and ProgressDisplayBar.
![screenshot_20140309090455](https://f.cloud.github.com/assets/6509348/2366771/c01a5a0e-a71c-11e3-8731-7c786f02cb57.png)