improving accessibility of tables

[StephDriver]

This will take some time!

Each table has a comment above it, so that it can be identified for work, and I can track which ones I've reviewed at any point.

right at the end of this, before merging, the comments will be removed.

closes #4055

[StephDriver]

Process:

• find tables and add comment above each.
• first review - expand comment to note obvious issues, and if none, which type of table (see below)
• fix obvious issues, and update comment to type of table.
• for each type of table, review in more detail, and fix any a11y markup required.
• Review all as to whether captions and summaries are required (probably not for our use, but check).
• remove the comments

Types of table (as per WCAG guidelines):

• V1 - One header (either row or column)
• V2 - header row and column row
• V3 - Irregular headers
• V4 - Multilevel headers