Breadcrumb: options for items that point to 404 (pagenotfound)

The breadcrumb path that the plugin renders may contain links that point to the pagenotfound url, in other words the user will get a 404 if they click on those items. This happens mostly in content driven sections of sites, like for example the url /news/2018/09/item1, where it's common practice to have the month and day (2018, 09) point to the pagenotfound, since there may be no use for having landing pages for these.

This issue is about enhancing the plugin to expose a new configuration parameter, governing what to do in cases like the above. At the moment I'm thinking of a parameter named "operationModeFor404s" with 2 possible values: "hide" and "unlink". So either the plugin hides items that point to 404 or renders them as plain text, so without a link.