title: iOS Game Center Group
body: <p>When I use <code>Group Leaderboard</code> in <code>Game Center</code> do I need to use "grp" prefix in id's enumerated in my app?
  <br>In other words if I will set up my existing game to use <code>Group Leaderboard</code> do I need to add "grp" prefix to each id in my app?</p>