add an allowlist signup page

[bunnybones1]

People should be able to sign up for the airdrop on a simple dedicated page, before the sale begins.
Once the sale begins, the signup page should be inaccessible, and the purchase page should show an authenticated user if they're approved or not.

We should think about, for the purposes of this demo, how people should be able to signup and purchase during the same time period, if possible