A Two-cohort, Open-label, Single-arm, Multicenter Study to Evaluate Efficacy, Safety and Tolerability, Pharmacokinetics and Pharmacodynamics of Emapalumab in Children and Adults with Macrophage Activation Syndrome (MAS) in Still’s Disease (Including Systemic Juvenile Idiopathic Arthritis and Adult Onset Still’s Disease) or with MAS in Systemic Lupus Erythematosus