Lumo’s new direct service between London Euston and Stirling launched just months ago, and it is already regularly selling out services.We stepped on board one of the recently refurbished trains to see what the six-hour journey to the historic Scottish city was like. London Euston has long been a hub for travel between the UK's capital and Scotland, but the new Lumo service has opened London up to a string of smaller communities along the West C…