[fix bug 969039] Change moderated group's join notification.
[fix bug 984298] Check that identifier exists before cleaning.
Merge pull request #862 from glogiotatidis/984298

[fix bug 984298] Check that identifier exists before cleaning.
Merge pull request #836 from glogiotatidis/969039-3

[fix bug 969039] Change moderated group's join notification.
[Fix bug 980887] Speed up browsing large groups