feature: crypto wallets and crypto donation page

closes #1 (closed)

this is a (basic) implementation of the /cryptocurrency page. it lists the crypto wallet names and addresses (without javascript), and presents a crypto donation form. the crypto form does its own validation, and checks that the estimated donation date isn't in the past, that the first and last name fields are empty if the donation isn't anonymous, and ensures that the first and last name fields are empty if the donation is anonymous.

there is no integration with civi, or the civi mock repository (yet)

i don't want to start merging MRs without at least a minimal CI setup, so this is blocked by #5 (closed)