Be able to see archived ideas

[vincentfretin]

Site administrators and moderators can archive an idea. The idea and the comments become visible only by the creator and administrators.
The other users have an insufficient privilege error. Like here:
https://afpy.nova-ideo.com/Bacs-de-tri-et-reduction-des-dechets/@@index#comment-8083978026344796741
It would be good to have a message that says the idea is archived and you can't see it because of that.

But I'd prefer to still be able to consult the idea and the comments but not add any new comments, and the idea is accessible only if you search for archived ideas.