Make Link and IconButton inherit from Button privately

Each part of the code deals with either Links or IconButtons, but
not both: the base class is only used to share implementation and
not interface. Make this explicit by doing private inheritance.

src/iconbutton.h

@@ -8,25 +8,27 @@
 class GMenu2X;
 class Surface;
 
-class IconButton : public Button {
+class IconButton : private Button {
 public:
 	IconButton(GMenu2X *gmenu2x, Touchscreen &ts,
 			const std::string &icon, const std::string &label = "");
 	virtual ~IconButton() {};
 
 	virtual void paint();
-	virtual bool paintHover();
 
 	virtual void setPosition(int x, int y);
 
 	void setAction(function_t action);
 
+	// Expose some Button functionality:
+	SDL_Rect getRect() { return Button::getRect(); }
+	bool handleTS() { return Button::handleTS(); }
+
 private:
-	void updateSurfaces();
+	void recalcSize();
 
 	GMenu2X *gmenu2x;
 	std::string icon, label;
-	void recalcSize();
 	SDL_Rect iconRect, labelRect;
 
 	Surface *iconSurface;