Updated latest scss changes from Font-Awesome


Imported latest scss infos from: https://github.com/FortAwesome/Font-Awesome/blob/22aa51f2a692de236f8688aa859b5ba9dd1b7f29/sass/font-awesome.scss

Fixes some bugs that have been identified. E.g. removing reference to unexisting font (https://github.com/FortAwesome/Font-Awesome/issues/233) by removing line
`font-url("#{$font_path}.svgz#FontAwesomeRegular") unquote("format('svg')"),`