Make it possible to restore dock widgets that are floating and NotDocked

Make it possible to restore dock widgets that are floating and NotDocked:

auto paragraphsDock = new QDockWidget(tr("Paragraphs"), this);
paragraphsDock->setObjectName("ParagraphsDock");

if (!restoreDockWidget(paragraphsDock))
   {
   paragraphsDock->setAllowedAreas(Qt::NoDockWidgetArea);
   paragraphsDock->setFloating(true);
   addDockWidget(Qt::NoDockWidgetArea, paragraphsDock);
   }

I will add example dockwidgets.zip into attachments part.
Step to reproduce this behavior :
1. Run dockwidgets.zip project
2. Move "Customers" dock widget to left dock area. Resize it.
3. Move "Paragraphs" dock widget somewhere. Resize it.
4. Close application. (It will save current window state in "closeEvent").
5. Open application. (It will restore saved states in "MainWindow" constructor).
6. Observe, that  "Customers" dock widget restores it size and position, where it was docked, and "Paragraphs" do not restore anything.