implement entire project in nodes

Project items are now represented directly in nodes opening up more versatility and possibilities. This is the first iteration of this and will be buggy. Need to test thoroughly.

app/node/output/track/tracklist.cpp

@@ -27,7 +27,7 @@
 
 namespace olive {
 
-TrackList::TrackList(ViewerOutput *parent, const Track::Type &type, const QString &track_input) :
+TrackList::TrackList(Sequence *parent, const Track::Type &type, const QString &track_input) :
   QObject(parent),
   track_input_(track_input),
   type_(type)
@@ -136,7 +136,7 @@ void TrackList::UpdateTrackIndexesFrom(int index)
 
 NodeGraph *TrackList::GetParentGraph() const
 {
-  return static_cast<NodeGraph*>(parent()->parent());
+  return parent()->parent();
 }
 
 const QString& TrackList::track_input() const
@@ -149,9 +149,9 @@ NodeInput TrackList::track_input(int element) const
   return NodeInput(parent(), track_input(), element);
 }
 
-ViewerOutput *TrackList::parent() const
+Sequence *TrackList::parent() const
 {
-  return static_cast<ViewerOutput*>(QObject::parent());
+  return static_cast<Sequence*>(QObject::parent());
 }
 
 int TrackList::ArraySize() const