Add rel=nofollow to various internal search links to prevent Google from
attempting to crawl things like `<tag> status:deleted` or `approver:<name>`
searches.
* Fix the artist URLs field not being prefilled when clicking
"Create new artist" in the "Fetch source data" box.
* Fix the artist name field not being prefilled when clicking
"Create new artist entry" on the /artists/show_or_new?name=<name> page.
* Fix access denied error when anonymous users open /artists/show_or_new.
* When the artist doesn't exist, take user to "artist doesn't exist"
page instead of redirecting to /artists/new.
