Fix reload command, use generator IDs

src/main/java/com/dfsek/terra/TerraWorld.java

@@ -106,7 +106,9 @@ public class TerraWorld {
 
     public static synchronized void invalidate() {
         map.clear();
-        loaded.clear();
+        for(WorldConfig config : loaded.values()) {
+            config.load(); // Reload all stored WorldConfigs
+        }
     }
 
     public static int numWorlds() {