bundle fonts

[ddiss]

This project is usable without internet access, with the exception of the Poppins font, which gets pulled down from Google.
Poppins appears to be licensed under OFL-1.1, so I think it'd make sense to just bundle it as a git submodule.

This would also be privacy preserving, given that https://developers.google.com/fonts/faq#what_does_using_the_google_fonts_api_mean_for_the_privacy_of_my_users states:

The Google Fonts API logs the details of the HTTP request, which includes
the timestamp, requested URL, and all HTTP headers (including referrer
and user agent string) provided in connection with the use of our CSS API.