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/node/input/media/media.cpp

@@ -37,12 +37,12 @@ void MediaInput::Release()
 
 StreamPtr MediaInput::footage()
 {
-  return footage_input_->get_value(0).value<StreamPtr>();
+  return footage_input_->get_value_at_time(0).value<StreamPtr>();
 }
 
 void MediaInput::SetFootage(StreamPtr f)
 {
-  footage_input_->set_value(QVariant::fromValue(f));
+  footage_input_->set_value_at_time(0, QVariant::fromValue(f));
 }
 
 bool MediaInput::SetupDecoder()