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

plus I did a little more commenting and refactoring
"There's no way we should do that because it'll make my IDE show wavy red underlines everywhere" is definitely a thing I've been told by co-workers.  One thing we might do to appease the IDE crowd is have a global constant called ``c`` and then instead of saying ``ATTENDEE_BADGE`` we'd say ``c.ATTENDEE_BADGE``, etc.  That would stop wavy red underlines without being much more verbose, since I would far prefer ``c.ATTENDEE_BADGE`` to ``config['attendee_badge']`` in terms of verbosity and whatnot.  We could even combine this with the ``State`` class.

That would definitely be more idiomatic, since most people don't do the global constants thing that we're doing, which kind of grew organically out of having those constants defined in our Python code and then later moved into a config file.

But I definitely don't want to make that change for this year since it would be a huge refactor to make (and is purely aesthetic), so maybe we can put this as a tentative todo item for next year.