* add a system_font_ui setting on the server
* Plug the system_font_ui on the front-end
* add EN/FR locales for the new setting
* put Roboto after all other fonts
* remove trailing whitespace so CodeClimate is happy
* fix user_spec.rb
* correctly write user_spect this time
* slightly better way of adding the classes
* add comments to the system-font stack for clarification
* use .system-font for the class instead
* don't use multiple lines for comments
* remove trailing whitespace
* use the classnames module for consistency
* use `mastodon-font-sans-serif` instead of Roboto directly
