artists: normalize urls added to artist entries.

When a URL is added to an artist entry, normalize it to a standard form.

Artist URLs have both a `url` column and a `normalized_url` column. The
`normalized_url` is used for artist finding and the `url` is the raw URL
entered by the user. Previously only the `normalized_url` field was
normalized; now the URL entered by the user is also converted to a
normalized form.

This means that if an URL like this is added to an artist entry:

* http://www.pixiv.net/member.php?id=1234
* http://www.pixiv.net/en/users/1234
* http://www.twitter.com/DanbooruBot/
* http://mobile.twitter.com/DanbooruBot/

It will get normalized to this:

* https://www.pixiv.net/users/1234
* https://twitter.com/DanbooruBot

This fixes problems with duplicate URLs being added to artist entries
because URLs weren't normalized to a single form.

app/logical/source/url/pixiv.rb

@@ -136,8 +136,7 @@ module Source
 
     def profile_url
       if user_id.present?
-        # "https://www.pixiv.net/users/#{user_id}"
-        "https://www.pixiv.net/member.php?id=#{user_id}"
+        "https://www.pixiv.net/users/#{user_id}"
       elsif username.present?
         "https://www.pixiv.net/stacc/#{username}"
       end