Unify link styles

[tiiavalt]

Is your feature request related to a problem? Please describe. Epimetheus' current link styles are a bit outdated according to the UI pictures.

Describe the solution you'd like Let's unify the link styles so they match the UI pictures and there's no duplicate code.

-- The result

• Unified link styles and removed redundant code
• Fixed MainNav's link styles
• Added accessible focus style for footer's links
• Refactored Breadcrumbs

There are currently no styles for :visited links even though it appears in UI pictures. The visited link's color is something between grey and dark green and it's not one of Epimetheus' colors so visited styles were not added yet.