#338: registration confirmation has a link to the confirmation page

plus I did a little more commenting and refactoring
I got rid of ``constants.py`` since at this point the main thing in it is the ``State`` class which is for defining properties which change over time.  So it was kind of a misnomer to name it ``constants`` since it's primarily for non-constant variables.  (Most of what ``constants.py`` was for was for storing enums which are now stored in our config files anyway.)