artists: redact version histories of banned artists.

Fix names and urls of banned artists being visible in Google through
artist version pages.

app/controllers/artist_versions_controller.rb

@@ -3,7 +3,7 @@ class ArtistVersionsController < ApplicationController
 
   def index
     set_version_comparison
-    @artist_versions = ArtistVersion.paginated_search(params)
+    @artist_versions = authorize ArtistVersion.visible(CurrentUser.user).paginated_search(params)
     @artist_versions = @artist_versions.includes(:updater, artist: :urls) if request.format.html?
 
     respond_with(@artist_versions)

app/controllers/artists_controller.rb

@@ -30,7 +30,7 @@ class ArtistsController < ApplicationController
   def index
     # XXX
     params[:search][:name] = params.delete(:name) if params[:name]
-    @artists = authorize Artist.paginated_search(params)
+    @artists = authorize Artist.visible(CurrentUser.user).paginated_search(params)
     @artists = @artists.includes(:urls, :tag) if request.format.html?
 
     respond_with(@artists)