The mythical city of Camelot bears a striking resemblence to Las Vegas’ Excalibur hotel. The legendary Lady of the Lake is accompanied by a team of cheering “Laker Girls.” When our heroes get to France, they’re greeted by everyone from a mime to Les Miz’s Eponine. These are just a handful of the gags scattered throughout the appealing Spamalot!, now playing to eager crowds at the National Theatre. Full disclosure: This reviewer is not a…