Back in the U.S.S.Wizard (or Added going back functionality via the 'Previous' buttons)

@codesliced Added functionality to make the `Previous` buttons work. There are still some known issues around fields getting repopulated (those fixes are a sort of different issue, for a separate branch). The browser's back button currently works better, but this is a first step and gets us away from the `enrollment_start` thing I had done earlier (i.e. Moved the first form into the Wicked wizard flow)