use isSubtitles itemKey for subtitles

pandora/item/models.py

@@ -1249,10 +1249,11 @@ class Item(models.Model):
         return icon
 
     def load_subtitles(self):
-        if not utils.get_by_id(settings.CONFIG['layers'], 'subtitles'):
+        subtitles = utils.get_by_key(settings.CONFIG['layers'], 'isSubtitles', True)
+        if not subtitles:
             return False
         with transaction.commit_on_success():
-            layer = 'subtitles'
+            layer = subtitles['id']
             Annotation.objects.filter(layer=layer,item=self).delete()
             offset = 0
             language = ''

pandora/item/utils.py

@@ -70,6 +70,9 @@ def get_positions(ids, pos):
             pass                                    
     return positions
 
-def get_by_id(objects, id):
-    obj = filter(lambda o: o['id'] == id, objects)
+def get_by_key(objects, key, value):
+    obj = filter(lambda o: o.get(key) == value, objects)
     return obj and obj[0] or None
+
+def get_by_id(objects, id):
+    return get_by_key(objects, 'id', id)