Static site integration

[anjackson]

Based on #48

This pull request integrates the static site builder from ukwa/ukwa-site, making it possible to manage the textual website content via a simple CMS rather than everything being inside the UKWA-UI Java project.

To Do

• [x] Some level of developer documentation, so it's clear what's what.
• [x] End user documentation/video showing how to edit content. e.g. editor is at https://ukwa-site.netlify.app/admin/ and uses GitHub etc.
• [x] Ensure website is complete/matches up with the current site.
• [x] Fix link in main menu, so it goes to the new Categories view via Collections redirect.
• [x] Probably take out the joke error page images e.g., which can be seen directy at https://dev.webarchive.org.uk/img/404/
• [x] Some pages are missing, i.e. translations not carried over yet.
• [x] Cookie banner link broken <a href="<no value>">cookie policy</a>
• [x] Make .cookie-cont row like margin:0; background-color: white so it looks okay and passes aXe contrast test.
• [x] Give white text in banner a #2e6dd9 background to pass aXe contrast test?
• [x] Make the button outlines a bit less heavy.
• [x] Give View buttons full names? e.g. View French In London? or maybe via aria/alt? Yes, aria-label can give full description.
• [x] Use exactly the same href link for the two Home buttons.
• [x] Strip out any DEV-specific hacks ahead of merging.

[anjackson]

Note that most of these changes are actually due to updating the API at the same time! The static pages changes are almost all hidden in the switch from nginx to ukwa-site.