DailyUI 004

On to day 4 of the #DailyUI challenge. I added a back button because it is always missing on calculators. I hate it when you enter a wrong number and have to start all over. The ability to delete single characters and retype is something I wish all calculators had. Also added a field showing the sequence of numbers and functions input. Another way to catch mistakes as well as check where you are if you are inputting a long series of computations.