Design of a part of a clinical trial called A Randomized, Double-blind, Multicenter Study of Subcutaneous Secukinumab, Assessing Psoriasis Area and Severity Index (PASI) Response and Maintenance of Response in Subjects With Moderate to Severe Chronic Plaque-type Psoriasis on Either a Fixed Dose Regimen or on a Retreatment at Start of Relapse Regimen