provide type information for Queue messages

Child extractors are now directly constructed with Extractor.from_url()
if the extractor class is known beforehand, instead of using
extractor.find() and searching through all possible extractor classes.

gallery_dl/extractor/photobucket.py

@@ -64,6 +64,7 @@ class PhotobucketAlbumExtractor(Extractor):
 
         if self.config("subalbums", True):
             for album in self.subalbums():
+                album["_extractor"] = PhotobucketAlbumExtractor
                 yield Message.Queue, album["url"], album
 
     def images(self):