Improve messaging and functionality for user registration

[neagle]

Is your feature request related to a problem?

Now that we have email activation required for new users, we have the inevitable problem of some users who do not receive their confirmation emails, or get stuck at some part of the registration process. Whether the problem is the confirmation message getting sent to the spam folder, or the user entering a typo for their email address, this presents a brick wall to people we'd like to see able to attend the event. Currently, the messages provided by the Devise confirmable module are a little too terse: we don't show the email address the confirmation message will come from, or provide any instructions for troubleshooting (like checking the spam folder), or provide a link to re-send the confirmation email.

Describe the feature you'd like to see on the Go Congress Website.

...We should do some/all of those things! And we should ideally provide an email link to the registrar and/or webmaster so people can ask for help. We're a small event and want to make sure everyone who's interested can come. :) Unfortunately, customizing Devise's messages with more than just text strings isn't trivial (or wasn't when I tried), so including something like a re-activation link can be trickier than it feels like it ought to be. But we need to figure out how!