#761 Restore permission group in sync with limbo players

- Couple AuthGroupHandler closer to the LimboService: whenever a limbo player is restored, the auth group should be restored as well. This fixes some consistency issues.
- Move AuthGroupHandler into limbo package and make it package-private
- Change permission handler to skip any empty groups (prevents odd command output e.g. for BukkitPermissions)

src/main/java/fr/xephi/authme/process/unregister/AsynchronousUnregister.java

@@ -8,8 +8,6 @@ import fr.xephi.authme.datasource.DataSource;
 import fr.xephi.authme.events.UnregisterByAdminEvent;
 import fr.xephi.authme.events.UnregisterByPlayerEvent;
 import fr.xephi.authme.message.MessageKey;
-import fr.xephi.authme.permission.AuthGroupHandler;
-import fr.xephi.authme.permission.AuthGroupType;
 import fr.xephi.authme.process.AsynchronousProcess;
 import fr.xephi.authme.security.PasswordSecurity;
 import fr.xephi.authme.service.BukkitService;
@@ -50,9 +48,6 @@ public class AsynchronousUnregister implements AsynchronousProcess {
     @Inject
     private TeleportationService teleportationService;
 
-    @Inject
-    private AuthGroupHandler authGroupHandler;
-
     @Inject
     private CommandManager commandManager;
 
@@ -123,7 +118,6 @@ public class AsynchronousUnregister implements AsynchronousProcess {
                 applyBlindEffect(player);
             });
         }
-        authGroupHandler.setGroup(player, AuthGroupType.UNREGISTERED);
         service.send(player, MessageKey.UNREGISTERED_SUCCESS);
     }