keyframeview: implemented transforming keyframe times to and from sequence time

Since the node graph can have transform cross nodes, input keyframes may occur
at a different times requiring transforming between sequence time and media
time. This commit implements such a mechanism in all UI classes that need it.

app/widget/curvewidget/curvewidget.h

@@ -11,7 +11,7 @@
 #include "widget/nodeparamview/nodeparamviewwidgetbridge.h"
 #include "widget/timebased/timebased.h"
 
-class CurveWidget : public TimeBasedWidget
+class CurveWidget : public TimeBasedWidget, public TimeTargetObject
 {
   Q_OBJECT
 public:
@@ -31,6 +31,8 @@ protected:
   virtual void TimebaseChangedEvent(const rational &) override;
   virtual void ScaleChangedEvent(const double &) override;
 
+  virtual void TimeTargetChangedEvent(Node* target) override;
+
 private:
   void UpdateInputLabel();