Add Friendly Fire permission for parties

This removes the friendly fire config option previously created
Both attacker and defender must have this option

Closes #648

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

@@ -689,4 +689,12 @@ public final class Permissions {
     public static boolean smelting(Player player) {
         return hasPermission(player, "mcmmo.skills.smelting");
     }
+
+    /*
+     * MCMMO.PARTY.*
+     */
+
+    public static boolean friendlyFire(Player player) {
+        return hasPermission(player, "mcmmo.party.friendlyfire");
+    }
 }