Lyfjarannsóknin: CNTO1275CRD3003 - EudraCT number: 2010-022760-12. A Phase 3, Randomized, Double-blind, Placebo controlled, Parallel-group, Multicenter Study to Evaluate the Safety and Efficacy of Ustekinumab Maintenance Therapy in Subjects with Moderately to Severely Active Crohn’s Disease (IMUNITI)