window manager: inverting all windows' visibility

Introducing a method that makes all visible windows invisible and vice-
versa.

DemoApp.cpp

@@ -130,6 +130,10 @@ namespace krikkel::NCurses
                         windowManager->updateLayout();
                         windowManager->refresh();
                         break;
+                    case KEY_F(4):
+                        windowManager->invertWindowsVisibility();
+                        windowManager->updateLayout();
+                        windowManager->refresh();
                     case KEY_F(5):
                         windowManager->refresh();
                         break;

TilingWindowManager.cpp

@@ -65,6 +65,27 @@ namespace krikkel::NCurses
         }
     }
 
+    void TilingWindowManager::invertWindowsVisibility()
+    {
+        list<WindowStackElement> originallyVisibleStack(visibleStack);
+        list<WindowStackElement>::iterator originallyVisibleStackIterator = originallyVisibleStack.begin();
+        visibleStack.clear();
+
+        for(WindowStackElement currentWindowElement : stack)
+            if(originallyVisibleStackIterator != originallyVisibleStack.end()
+                    && currentWindowElement == *originallyVisibleStackIterator)
+            {
+                currentWindowElement.first->hidden = true;
+                ++originallyVisibleStackIterator;
+                continue;
+            }
+            else
+            {
+                currentWindowElement.first->hidden = false;
+                visibleStack.push_back(currentWindowElement);
+            }
+    }
+
     int TilingWindowManager::resize(int rows, int cols)
     {
         int result = Window::resize(rows, cols);

include/kNCurses/TilingWindowManager.hpp

@@ -45,6 +45,7 @@ namespace krikkel::NCurses
 
             void hideWindow(Window *window);
             void showWindow(Window *window);
+            void invertWindowsVisibility();
 
         protected:
             /// @todo rename to `nCursesMutex`?