reworked and vastly improved snapping subsystem

app/widget/keyframeview/keyframeview.h

@@ -63,6 +63,11 @@ public:
     return selection_manager_.GetSelectedObjects();
   }
 
+  const QVector<KeyframeViewInputConnection*> &GetKeyframeTracks() const
+  {
+    return tracks_;
+  }
+
   virtual void SelectionManagerSelectEvent(void *obj) override;
   virtual void SelectionManagerDeselectEvent(void *obj) override;
 

app/widget/keyframeview/keyframeviewinputconnection.h

@@ -50,7 +50,7 @@ public:
 
   void SetYBehavior(YBehavior e);
 
-  const QVector<NodeKeyframe*> GetKeyframes() const
+  const QVector<NodeKeyframe*> &GetKeyframes() const
   {
     return input_.input().node()->GetKeyframeTracks(input_.input()).at(input_.track());
   }