[STAN-1093] Add basic accessibility checking to most pages

[roc]

Adds top level a11y checks

• Auditing future standards brought up an aria value violation
• have added clickthroughs with checks for those values
• wait directives seem to, begrudgingly, be necessary to avoid race conditions

Reorders static pages, tests for a11y

The a11y checker made a reasonable point about heading order in our static pages. I've shuffled the content in those pages so that the table on contents comes after the page title:

Before

After