[FIX] Unlink creator when deleting conference
[FIX] Unlink creator when deleting conference

pferreir/indico,OmeGak/indico,pferreir/indico,OmeGak/indico,DirkHoffmann/indico,OmeGak/indico,DirkHoffmann/indico,mvidalgarcia/indico,DirkHoffmann/indico,mic4ael/indico,mvidalgarcia/indico,mic4ael/indico,pferreir/indico,pferreir/indico,ThiefMaster/indico,mvidalgarcia/indico,indico/indico,indico/indico,ThiefMaster/indico,DirkHoffmann/indico,indico/indico,mvidalgarcia/indico,ThiefMaster/indico,indico/indico,ThiefMaster/indico,mic4ael/indico,mic4ael/indico,OmeGak/indico