Enable placeholder usage within Sass & SCSS templates

[brenner-company]

A small change that allows us to use the icon-font styling as a placeholder within Sass & SCSS templates so it can be easily extended. For example: elements that are maintained externally (in an extension or a plugin) and are not changeable (regarding HTML structure).

As an example (using SCSS template):

.element-of-extension {
  &:before {
    @extend %[base name]-font-style; // extends all the necessary icon-font styling
    @extend .[prefix]-[icon name]; // extends specific icon
  }
}