When Nikki Janicek sprints from the 200-degree sauna out into the 100-below darkness wearing nothing but bunny boots, at least she's not alone.She already has survived months of solitary confinement, a forced swim with sharks and a scary journey to the South Pole. Now she's a member of The 300 Club, an exclusive group of people on the planet who have endured a 300-degree temperature swing in a matter of seconds.It's all part of her training for a...