Fix link colors

[Neraste]

This PR rationalizes the use of colors for generic sets (neutral, primary, info, etc.), by specifying:

• background color;
• background selection color;
• text color;
• text selection color;
• text quote color;
• link color;
• link hover color; and
• link focus color.

This solves some extra margins induced by the text class introduced by #281.

Side effect: default coloring was mostly removed, so an item without a generic color specified (neutral, primary, etc.) will have the default browser colors.