Tidy up entity geometry stuff:

- Add a getCentre method for entities to GeometryUtils
- Replace getPositionEyes(0) with getPositionEyes(1) since it's more efficient, and by definition they must be the same
- Remove all the silly getEntityBoundingBox().minY stuff, this bug has been fixed since 1.8! (which begs the question: if it was considered a bug, how on earth did it go unfixed for that long?)
- A few other small things

src/main/java/electroblob/wizardry/spell/Whirlwind.java

@@ -41,7 +41,7 @@ public class Whirlwind extends SpellRay {
 		// Left as EntityLivingBase because why not be able to move armour stands around?
 		if(target instanceof EntityLivingBase){
 			
-			Vec3d vec = target.getPositionVector().add(0, target.getEyeHeight(), 0).subtract(origin).normalize();
+			Vec3d vec = target.getPositionEyes(1).subtract(origin).normalize();
 
 			if(!world.isRemote){