Add setting for contact roster name

And only exchange contacts when ejabberd integration is enabled

app/services/create_account.rb

@@ -15,7 +15,7 @@ class CreateAccount < ApplicationService
 
     if @invitation.present?
       update_invitation(user.id)
-      exchange_xmpp_contacts
+      exchange_xmpp_contacts if Setting.ejabberd_enabled
     end
   end