fixed Player loosing ability to use commands etc.
CraftPlayer.getPlayer() returns itself so the OfflinePlayer saved in the UserBase has to always be a CraftOfflinePlayer (not possible because Bukkit.getOfflinePlayer(...) returns CraftPlayer when online)
OR always update the CraftPlayer when he gets a new Connection. (too complicated)
So we just save the userName in the UserBase and get the OfflinePlayer when needed from directly Bukkit.