Adding new fonts (Fira Code Stylistic Sets)

Hi.

It appears that blink.sh does not accept the .monaco-editor CSS property that Fira Code uses to enable stylistic sets. See https://github.com/tonsky/FiraCode/wiki/How-to-enable-stylistic-sets#css

I added the appropriate lines to the Fira Sans template from https://github.com/blinksh/fonts/blob/master/Fira%20Code.css and tried to import the resulting CSS into blink.sh. However, the alternatives were not working.

Start with the Fira Code stylistic-sets wiki and the fonts repository's Fira Code.css template, then trace how blink.sh imports and applies that CSS. Confirm where the .monaco-editor property is handled and define completion as the stylistic-set alternatives working after importing the resulting CSS.

Written by the indexing model from the issue text.