refs #325, as preparation to reduce loading I need to find out when an info area is visible.

Existing functions visible() / isHidden() are not suitable, as those represent "technical visibility".
We need a logical visibility telling us if the user can see / has selected the corresponing dockable widget.

* New base class info area (where dockable widgets are placed)
* Adjusted derived component (currently 1)
* Cleaned up old code in floatAllWidgets

src/blackgui/dockwidgetinfobar.h

@@ -18,6 +18,8 @@ namespace BlackGui
 {
 
     //! Class for dock widgets in the info area, containing some specialized functionality
+    //! \sa CDockWidgetInfoArea
+    //! \sa CInfoArea
     class CDockWidgetInfoBar : public CDockWidget
     {
         Q_OBJECT