Add captcha to anonymous donation form

[jzongker]

Bots are submitting the B1 donation form in mass to search for valid credit card numbers. Let's add a basic captcha to it.

It doesn't need to be anything particularly robust. Just free (ideally an npm component we can just install) and if possible a simple "check a box" type captcha rather than a puzzle solving one.

[jzongker]

There's one big challenge to consider on this one. Churches will be using custom domains for b1 (hypothetical example: ironwoodchurch.com is an alias for ironwood.b1.church). That means we can not simply provide a white list of domains for third party services that require it, such as recaptcha.