Expose the double spinbox to ctkSliderWidget public API

It can be useful to move the spinbox somewhere else, but keeping the
links between the slider and spinbox.

Libs/Widgets/ctkSliderWidget.cpp

@@ -494,3 +494,10 @@ void ctkSliderWidget::setSpinBoxVisible(bool visible)
   Q_D(ctkSliderWidget);
   d->SpinBox->setVisible(visible);
 }
+
+// --------------------------------------------------------------------------
+QDoubleSpinBox* ctkSliderWidget::spinBox()
+{
+  Q_D(ctkSliderWidget);
+  return d->SpinBox;
+}

Libs/Widgets/ctkSliderWidget.h

@@ -23,6 +23,7 @@
 
 // Qt includes
 #include <QSlider>
+class QDoubleSpinBox;
 
 // CTK includes
 #include <ctkPimpl.h>
@@ -165,6 +166,13 @@ public:
   /// isSpinBoxVisible().
   bool isSpinBoxVisible()const;
 
+  ///
+  /// Sometimes it can be useful to have a direct control to the spinbox
+  /// To place it somewhere else that ctkDoubleSlider can't. Be careful
+  /// with what you do with the spinbox as ctkDoubleSlider might change
+  /// properties automatically.
+  QDoubleSpinBox* spinBox();
+
 public slots:
   /// 
   /// Reset the slider and spinbox to zero (value and position)