Pediatric Asthma Clinical Effectiveness study (PEACE). A Randomized, Double-Blind, Double Dummy, Parallel Group comparative clinical study of Salmeterol/Fluticasone propionate Inhalation Powder (50/100mcg BID) via DISKUS† with Oral montelukast (5mg QD) Chewable Tablets in Children 6-14 years of Age with Persistent Asthma