Support more YouTube URLs

The regular expression is also more strict, yet accepts the
youtu.be short URLs and user page URLs.

weboob/backends/youtube/video.py

@@ -28,3 +28,8 @@ class YoutubeVideo(BaseVideo):
     @classmethod
     def id2url(cls, _id):
         return 'http://www.youtube.com/watch?v=%s' % _id
+
+    def _get_shorturl(self):
+        return 'http://youtu.be/%s' % self.id
+
+    shorturl = property(_get_shorturl)