Add Playlist thumb alias to composite

plexapi/base.py

@@ -232,7 +232,7 @@ class PlexObject(object):
     def firstAttr(self, *attrs):
         """ Return the first attribute in attrs that is not None. """
         for attr in attrs:
-            value = self.__dict__.get(attr)
+            value = getattr(self, attr, None)
             if value is not None:
                 return value
 

plexapi/playlist.py

@@ -63,6 +63,11 @@ class Playlist(PlexPartialObject, Playable, ArtMixin, PosterMixin):
         for item in self.items():
             yield item
 
+    @property
+    def thumb(self):
+        """ Alias to self.composite. """
+        return self.composite
+
     @property
     def metadataType(self):
         if self.isVideo: