[Feature] Check the accessibility of the site

[eleanorscott97]

Description

• Can the site be navigated via the keyboard
• Do all images, tables and maps have alternative text
• Does most of the site do sensible things when used with a screen reader?

Acceptance Criteria
AC1: Site is keyboard accessible
AC2: Everything that needs an alternative text attribute, has an alternative text attribute
AC3: Site is mostly useable with a screen reader