Migrate icons to FontAwesome svg files (from the font file) #68

Latest FontAwesome version make available a package[1] where each individual icon is defined in a plain svg file. Given this I want to import only the needed svg files into a single svg defs files and use inline svg tags.

I started that conversion work in gorhill/uMatrix@c6e29be#diff-4de122c13cf2cc4e2364626b0acdb2c9.

[1] https://use.fontawesome.com/releases/v5.3.1/fontawesome-free-5.3.1-web.zip