Resolve "Integrate Font Awesome with Jekyll"

• Set Sass style to compressed to reduce the asset size that needs to be downloaded
• Make Font Awesome available via Sass.
  • Brands and icons from the solid style are available.
  • If other styles shall be activated they need to be included in general.scss.
  • Example icon usage: <i class="fas fa-car"></i>
• Import the external dependency via git submodules

Closes #16 (closed)