Moved some craftbukkit stuff down from WorldServer to World; should fix a few NPEs during generation, and saves on a lot of casting

By: Dinnerbone <dinnerbone@dinnerbone.com>

paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java

@@ -475,7 +475,7 @@ public final class CraftServer implements Server {
         return worlds.get(name.toLowerCase());
     }
 
-    protected void addWorld(World world) {
+    public void addWorld(World world) {
         worlds.put(world.getName().toLowerCase(), world);
     }