Gone are the days of air mattresses on the floor. Airbnb Inc. is now catering to the mega-wealthy with a new tier of luxury rentals. Airbnb Luxe went live Tuesday morning after long being teased, with 2,000 new listings on Airbnb’s website offering guests the chance to stay in some of the world’s most extravagant homes. Everything from entire islands to medieval castles and mansions decked out with water slides, dinosaur skulls, and archery ranges are up for rent.The average luxury listing has an asking price of $14,000 a week—but can go as high as $1 million a week for a private atoll near Tahiti that comprises 21 ... (full story)