Don't allow vanished players to block others from teleporting. Fixes #111.

src/main/java/com/massivecraft/factions/integration/Essentials.java

@@ -36,4 +36,8 @@ public class Essentials {
         }
         return true;
     }
+
+    public static boolean isVanished(Player player) {
+        return essentials.getUser(player).isVanished();
+    }
 }