Make site metadata accessible

[adamwoodnz]

Fixes #235

After trying various CSS display layouts (flex, grid, table) and failing to make the content display well and read well, this PR updates the markup to use a table so that screen reader users can use appropriate content navigation.

This is the approach suggested by the A11y team.

There should be no visual change.

Screenshots

Home

Desktop	Tablet	Mobile

Single

Desktop	Tablet	Mobile

NVDA transcripts

Home page

main landmark    list  with 1 item  table  with 3 rows and 2 columns  row 1  column 1  Site title
column 2  visited  link    Vogue
URL  row 2  link    vogue.com
Category  row 3  link    Publication

Single site page

main landmark    table  with 4 rows and 2 columns  row 1  column 1  Author
column 2  Condé Nast
Country  row 2  United States
Category  row 3  link    Publication
Published  row 4  October 2019

Testing

Browse the home page and single site pages using a screen reader, preferably JAWS or NVDA.
Focus the table using t then Ctrl+Alt+Arrows to navigate within the table.
Content should be read out with semantics as above.
Check for visual regressions, including various screen sizes and RTL.