Fix water level calculations when waterLevel > 127

This was caused by Java treating bytes as signed by default.

Thanks to @matt112986 for the research on this and for providing a test
map.

While fixing this, I also noticed that waterLevelSum doesn't need to be
a float.
Merge branch 'master' of https://github.com/Wickth/TerrainControl into features-merge

Conflicts:
	common/src/main/java/com/khorn/terraincontrol/generator/ChunkProviderTC.java