Add sendy integration

[slaporte]

Here are the old signup pages we need to swap out in weeklypedia-history:

lang	mailchimp	new signup
en	http://eepurl.com/MMlpX	https://weekly.hatnote.com/archive/en/index.html
de	http://eepurl.com/MMlG9	https://weekly.hatnote.com/archive/de/index.html
fr	http://eepurl.com/MMmVX	https://weekly.hatnote.com/archive/fr/index.html
ko	http://eepurl.com/MMm8n	https://weekly.hatnote.com/archive/ko/index.html
et	http://eepurl.com/MMnlf	https://weekly.hatnote.com/archive/et/index.html
sv	http://eepurl.com/MMTnP	https://weekly.hatnote.com/archive/sv/index.html
da	http://eepurl.com/Sko4L	https://weekly.hatnote.com/archive/da/index.html
it	http://eepurl.com/MQTPb	https://weekly.hatnote.com/archive/it/index.html
ca	http://eepurl.com/M7HU9	https://weekly.hatnote.com/archive/ca/index.html
eo	http://eepurl.com/_RE_X	https://weekly.hatnote.com/archive/eo/index.html
es	http://eepurl.com/br8NNj	https://weekly.hatnote.com/archive/es/index.html
fa	http://eepurl.com/br8TlT	https://weekly.hatnote.com/archive/fa/index.html
zh	http://eepurl.com/bsmGhT	https://weekly.hatnote.com/archive/zh/index.html
ur	http://eepurl.com/bsmG1P	https://weekly.hatnote.com/archive/ur/index.html
kn	http://eepurl.com/buxugf	https://weekly.hatnote.com/archive/kn/index.html
lv	http://eepurl.com/b0V-yj	https://weekly.hatnote.com/archive/lv/index.html
el	http://eepurl.com/b0WcUr	https://weekly.hatnote.com/archive/el/index.html
te	http://eepurl.com/b3EjMn	https://weekly.hatnote.com/archive/te/index.html
oc	http://eepurl.com/dxJIYf	https://weekly.hatnote.com/archive/oc/index.html
ru	http://eepurl.com/dxJJGn	https://weekly.hatnote.com/archive/ru/index.html
uk	http://eepurl.com/dxJKwf	https://weekly.hatnote.com/archive/uk/index.html