v2.9

• added: plugin setting to indicate if a group is hidden
• added: option to configure a group welcome message (#41)
• added: listing of the email invitations for groups (#42)
• added: option to join groups based on email domain (#43)
• added: option to relate groups (#44)
• fixed: layout issue in plugin settings
• fixed: you can no join groups you were invited for on the group profile page
• fixed: misleading translation for a group cleanup setting (#22)
• fixed: create group button showing up on some pages when setting was disabled (#35)