Update font-awesome to v6.4.2

[stephan-strate]

This pull requests updates font-awesome to the new major version v6. Therefore some minor changes needed to be made.

• From v6, there is no official cdn anymore. font-awesome recommends using kits or self-host the packages. I decided to use the cdnjs cdn
• Some icons got renamed, see here
  • fa-map-marker-alt -> fa-location-dot
  • fa-external-link-alt -> fa-up-right-from-square
  • fa-mobile-alt -> fa-mobile-screen-button
• Also the category names changed, see here
  • fas -> fa-solid
  • fab -> fa-brands
  • far -> fa-regular