sweeping node graph changes for new rendering pipeline

The new rendering pipeline strives to simplify the nodes themselves as much
as possible and move much of the logic to an external rendering engine. This
change removes all of the responsibilities that no longer belong to the
nodes themselves and will soon be folded into the renderer.

app/project/item/sequence/sequence.cpp

@@ -103,7 +103,7 @@ QString Sequence::duration()
     return QString();
   }
 
-  rational timeline_length = timeline_output_->length_output()->get_value(0, 0).value<rational>();
+  rational timeline_length = timeline_output_->length_output()->get_realtime_value().value<rational>();
 
   int64_t timestamp = olive::time_to_timestamp(timeline_length, video_params_.time_base());