• review use of tables across platform

From #4194 the following issues have been identified:

• Tables do not consistently have <th> tags for both rows and columns. This occurs in both tables that are part of the main template for the page, e.g. article dates shown on the material theme, and for tables within articles themselves.
• footnotes within the tables that are to be written under the table, rather than as endnotes are not working well.

Part of the problem here is that JATS allows for inaccessible tables to be specified, thus user content will not always produce accessible tables. The row/column headings should be specified in the JATS and then picked up so if it is not correct there, it won't be correct on the page either.

Therefore we should -

• ensure non-article (i.e. non user content) tables are accessible. Each data cell is expected to be understood in the context of one column header and one row header - so a single row of headers and a single column of headers for each table, using the <th> tag.
• add user content/jats issue to Phase 2 of A11y project.