A Randomized, Double-blind, Double-dummy, Placebo Controlled, Multicenter Study of Subcutaneous Secukinumab to Demonstrate Efficacy After Twelve Weeks of Treatment, Compared to Placebo and Etanercept, and to Assess the Safety, Tolerability and Long-term Efficacy up to One Year in Subjects With Moderate to Severe Chronic Plaque-type Psoriasis