Refactor stylesheets

Style Banner as full-width strip
  - stacks on small viewports
  - stretches to inline on wider viewports
  - logo display independant of title

Style article templates
  - allow title to stretch full page width
  - include data or optional subtitle in title banner
  - process titles with Markdown to get smart quotes

Add Open Sans to the fallback font stack.

Cleanup variable usage in component stylesheets

Set custom text selection colour

Remove logo link from the tabindex