SINGAPORE (Reuters) - Some start-ups are taking on one of air travel's last undisrupted bastions - the economy-class cabin. While first and business class travelers have long enjoyed comfort upgrades, there's been less attention to innovation at the rear of the plane. "We want to make travel memorable and comfortable for all of us, not just the top 1 percent," Alireza Yaghoubi, founder of Singapore-based AirGo, told a recent start-up conference to pitch his superlight economy-class seat. H