Add fallback for header when CSS Grid is not supported

[michaelbragg]

As CSS Grid is not currently supported, in full, by IE Edge and below and Mini Opera. We need to make it look acceptable.

[michaelbragg]

Desktop Safari

iOS Safari - Landscape

Opera Mini - Portrait

Opera Mini – Landscape

[michaelbragg]

Safari's issue looks to be with CSS Grid's handling of named columns. Not flexbox displaying the navigation items.