sources: factor out Source::URL::HentaiFoundry.

Add support for these URL types:

* http://pictures.hentai-foundry.com//s/soranamae/363663.jpg
* http://www.hentai-foundry.com/piccies/d/dmitrys/1183.jpg
* http://www.hentai-foundry.com/pic-149160.php
* http://www.hentai-foundry.com/user-RockCandy.php
* http://www.hentai-foundry.com/profile-sawao.php

These URL types are obsolete, but still present in some old posts.

app/logical/source/url/twit_pic.rb

@@ -28,6 +28,10 @@ class Source::URL::TwitPic < Source::URL
     url.host.in?(%w[twitpic.com o.twimg.com dn3pm25xmtlyu.cloudfront.net d3j5vwomefv46c.cloudfront.net])
   end
 
+  def site_name
+    "TwitPic"
+  end
+
   def parse
     case [domain, *path_segments]