Add scene duration filter (#313)

* Add scene duration filter

graphql/schema/types/filters.graphql

@@ -64,6 +64,8 @@ input SceneFilterType {
   rating: IntCriterionInput
   """Filter by resolution"""
   resolution: ResolutionEnum
+  """Filter by duration (in seconds)"""
+  duration: IntCriterionInput
   """Filter to only include scenes which have markers. `true` or `false`"""
   has_markers: String
   """Filter to only include scenes missing this property"""