By Jane Lanhee Lee HAINING, China, Feb 7 (Reuters) - A luggage trolley that converts into a seat and a pole with pads that props up sleepy passengers are just a couple of the gadgets intrepid Chinese have devised to help make their annual New Year train trips home a little more comfortable. About 200 million people in China are expected to take trains home for the New Year's holiday at the weekend in what has been described as the world's largest annual migration.