Change default fonts

[Garrick Aden-Buie]

So far, I've tried to keep the themes so that the "start from" the default xaringan theme and can be customized away.

But Droid Serif isn't officially part of Google Fonts anymore and causes problems with sysfonts::font_add_google(). I think the default fonts look interesting but are terrible for legibility in presentations to large audiences.

I like the Source Sans Family or Noto Sans Family. Both have wide support at many weights, languages and have corresponding serif and code fonts.