Fix BlackGui header includes

* Include only what is used
* Use forward declaration when possible
* Sorted includes

refs #598

src/blackgui/showhidebar.h

@@ -13,7 +13,12 @@
 #define BLACKGUI_SHOWHIDEBAR_H
 
 #include "blackgui/blackguiexport.h"
+
 #include <QFrame>
+#include <QObject>
+#include <QScopedPointer>
+
+class QWidget;
 
 namespace Ui { class CShowHideBar; }