colordialog/wheel/gradient: implemented basic UI components for color picking

app/widget/colorbutton/colorbutton.cpp

@@ -5,11 +5,13 @@
 ColorButton::ColorButton(QWidget *parent) :
   QPushButton(parent)
 {
+  color_ = Color(1.0f, 1.0f, 1.0f);
+
   connect(this, &ColorButton::clicked, this, &ColorButton::ShowColorDialog);
 }
 
 void ColorButton::ShowColorDialog()
 {
-  ColorDialog cd(nullptr);
+  ColorDialog cd(nullptr, color_, this);
   cd.exec();
 }

app/widget/colorbutton/colorbutton.h

@@ -3,6 +3,8 @@
 
 #include <QPushButton>
 
+#include "render/color.h"
+
 class ColorButton : public QPushButton
 {
   Q_OBJECT
@@ -15,6 +17,9 @@ signals:
 private slots:
   void ShowColorDialog();
 
+private:
+  Color color_;
+
 };
 
 #endif // COLORBUTTON_H