Add .nbmedias to get the nb of files in an album

sigal/gallery.py

@@ -472,6 +472,10 @@ class Album:
         return [self.gallery.albums[join(root_path, path)]
                 for path in self.subdirs]
 
+    @property
+    def nbmedias(self):
+        return len(self.medias) + sum(len(album) for album in self.albums)
+
     @property
     def url(self):
         """URL of the album, relative to its parent."""