Refactor related to #1106, #1107, #1109, #1113. Refactored the MDI control

of windows. This might introduce problems.

ApplicationCode/Application/RiaApplication.h

@@ -55,6 +55,7 @@ class RimViewWindow;
 class RimWellLogPlot;
 class RimWellAllocationPlot;
 
+class RiuMainWindowBase;
 class RiuMainPlotWindow;
 class RiuRecentFileActionProvider;
 
@@ -185,6 +186,7 @@ public:
 
     RiuMainPlotWindow*  getOrCreateAndShowMainPlotWindow();
     RiuMainPlotWindow*  mainPlotWindow();
+    RiuMainWindowBase*  mainWindowByID(int mainWindowID);
 
     static RimViewWindow* activeViewWindow();