Icons: Fix external link class specificity

- Header and footer external links exhibit the same behaviour as before
without the increased specificity on the body
- The 20px right padding is left for now
Iconds: Add additional comments
Icons: Update external link comments
Icons: Better specificity on rel external padding
Merge pull request #2106 from nschonni/fix-external-link-button-background

Icons: Fix external link class specificity