/artists: add wildcard, regex search to url field (#3900)

Allow searching the URL field by regex or by wildcard.

If the query looks like `/twitter/` do a regex search, otherwise if it
looks like `http://www.twitter.com/*` do a wildcard search, otherwise if
it looks like an url do an artist finder search, lastly if it looks like
`twitter` do a `*twitter*` search.

app/logical/sources/strategies/base.rb

@@ -153,7 +153,7 @@ module Sources
       end
 
       def artists
-        Artist.url_matches(normalize_for_artist_finder)
+        Artist.find_artists(normalize_for_artist_finder)
       end
 
       def file_url