Implement full check registration + win gift card flow

[davepeck]

When merged, closes #12 closes #13 closes #16

[davepeck]

It sorta made logical sense to make fireworks/banner updates a key part of this PR too. So here we are. When merged, also closes #18 too.

[davepeck]

[davepeck]

The "good path", where students provide a valid email for an active contest, is done working and tested. Now on to the edge cases.

[davepeck]

Still to do:

• On the good path, when a new gift card is generated, be sure to send an email that also contains the claim code.
• If user verifies their registration with a .edu address that does not match their expected school, show UI that asks them for an alternative. If the alternative is valid, finish the flow. Otherwise, keep asking until the user cancels.
• If user visits school landing page and there is no active contest, encourage registration (and mention when the previous contest ended, if any)
• If user verifies their registration but no contest is active, alter the validation link and email flow to simply say "validate my email" and bring them back to the site thanking them for their work.
• Make sure all text is still correct even in the no-active-contest path.
• Make sure that if a user verifies their registration before a contest closes, but validates their email after, we still issue a gift card tied to the correct contest.
• Make sure that errors in generating gift cards are reflected on the site, with a prominent link to reach out to customer support ([email protected]).
• Make sure everything looks good on the iphone too

[davepeck]

Absorbing #10 and #19 into this PR, too.