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/ArcaneJammer.java

@@ -109,7 +109,7 @@ public class ArcaneJammer extends SpellRay {
 
 			if(event.getWorld().isRemote){
 
-				Vec3d centre = event.getCaster().getPositionEyes(0).add(event.getCaster().getLookVec());
+				Vec3d centre = event.getCaster().getPositionEyes(1).add(event.getCaster().getLookVec());
 
 				for(int i = 0; i < 5; i++){
 					double x = centre.x + 0.5f * (event.getWorld().rand.nextFloat() - 0.5f);