Groupon has sold its one billionth “Groupon.” The online retail discount portal says the milestone puts it in the same group as Apple, McDonalds, Uber, The Beatles, Elvis and other brands and icons that have achieved the “billion-sold milestone.”   While the billionth Groupon sold was promotion for pizza in the St. Louis area, the company has had quite a bit of activity in other categories from travel to beauty.   For instance, Groupon has sold four million body hair removals and says it has...