Disable our healthbars when the plugin "HealthBar" is found

Adds #1477

src/main/java/com/gmail/nossr50/util/MobHealthbarUtils.java

@@ -40,7 +40,7 @@ public final class MobHealthbarUtils {
      * @param damage damage done by the attack triggering this
      */
     public static void handleMobHealthbars(Player player, LivingEntity target, double damage) {
-        if (!Permissions.mobHealthDisplay(player)) {
+        if (!mcMMO.isHealthBarEnabled() || !Permissions.mobHealthDisplay(player)) {
             return;
         }