Fix @cartes.data.gouv.fr/#25

* Only keep useful woff/woff2 fonts: http://davidensinger.com/2014/10/update-your-font-face-file-formats-to-just-use-woff-and-woff2/
* Fallback to system fonts: https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/
* Declare fonts with correct weight/style to avoid the change to all elements: http://stackoverflow.com/a/21614532
* Switch from Bold to SemiBold to be consistent with the use of Light by default