#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/test/java/fr/xephi/authme/service/CommonServiceTest.java

@@ -2,8 +2,6 @@ package fr.xephi.authme.service;
 
 import fr.xephi.authme.message.MessageKey;
 import fr.xephi.authme.message.Messages;
-import fr.xephi.authme.permission.AuthGroupHandler;
-import fr.xephi.authme.permission.AuthGroupType;
 import fr.xephi.authme.permission.PermissionNode;
 import fr.xephi.authme.permission.PermissionsManager;
 import fr.xephi.authme.permission.PlayerPermission;
@@ -41,9 +39,6 @@ public class CommonServiceTest {
     @Mock
     private PermissionsManager permissionsManager;
 
-    @Mock
-    private AuthGroupHandler authGroupHandler;
-
     @Test
     public void shouldGetProperty() {
         // given
@@ -113,17 +108,4 @@ public class CommonServiceTest {
         verify(permissionsManager).hasPermission(player, permission);
         assertThat(result, equalTo(true));
     }
-
-    @Test
-    public void shouldSetPermissionGroup() {
-        // given
-        Player player = mock(Player.class);
-        AuthGroupType type = AuthGroupType.LOGGED_IN;
-
-        // when
-        commonService.setGroup(player, type);
-
-        // then
-        verify(authGroupHandler).setGroup(player, type);
-    }
 }