Allow backwards navigation if a site fails to load

[raelg]

When navigating to a site that fails to load, the page should be added to the back-forward list so that it is possible to go back to the previous site and navigate to other links.

E.g., if navigating to a broken site from a Google search then the user should be able to go back to Google search results to check other links.

I have a PR with a potential fix: raelg#1, however, this depends on this PR being merged first: #1677

The fix uses the local web server to serve the error page (so it is added to the back-forward list), with the url extracted from a query parameter and shown in the url bar. To prevent someone from misusing this feature (url override), a secret local value is created which must match another query parameter.

┆Issue is synchronized with this Jira Task