What’s going on here? Thomas Cook, the world’s oldest travel company, has abruptly shut down, leaving 500,000 stranded passengers around the world feverishly Googling “max number of days it’s ok to wear the same socks.”  All 21,000 of its employees’ jobs at risk. FYI: The 178-year-old U.K.-based firm specialized in low-cost package vacations, bundling flights and accommodations in over…