Birkenstock is stepping into a new category. The German-based maker of the iconic sandals is rolling out a line of personal care products it says are “developed and produced in Germany using the finest natural ingredients and certified in accordance with stringent natural cosmetic standards.”    Birkenstock Natural Care was unveiled at Vivaness, an international trade fair for natural and organic personal care that was held in Nuremberg, Germany last month. It will be available internationa...