As the Disney blockbuster ends its three-year run at Theatre Royal Drury Lane in London, actor Samantha Barks pays tribute to its devoted audience Sometimes it has been a flurry and at others a blizzard. For three years theatregoers dressed in shades of Elsa blue have descended on Covent Garden for Disney's blockbuster stage musical Frozen. On Sunday, it finally came to an end as the guards opened up the gates of Lon…