MBS-9607: Rewrite MusicBrainz not found pages in React/JSX

[spellew]

Replaced all the not_found.tt files with equivalent templates written in React/JSX. Accepted on Google Code-In by yvanzo.

[yvanzo]

Depends on PR #599.

[mwiencek]

I think we should create a reusable NotFound component to reduce some of the duplication here. Here's an example of what that would look like:

const EditNotFound = () => (
  <NotFound
    title={l('Edit Not Found')}
    message={l('Sorry, we could not find an edit with that edit ID. You may wish to try and perform an {search_url|edit search} instead.', {__react: true, search_url: '/search/edits'})}
  />
);

[mwiencek]

Please don't change the strings unless necessary. I saw you changed {url|search} to {search_url|search} and had to go through all the rest to make sure there weren't other changes. These changes require translators to retranslate things for no reason.

(No need to push fixes, I'm taking care of it.)

[mwiencek]

Fixed it so that the pages actually still 404 in 9902927.