float the selection panel over the game world instead of a side column

src/ui/MainWindow.h

@@ -28,7 +28,7 @@ struct ParsedReplay;
 class Simulation;
 class GameWorldView;
 class HeaderBar;
-class SelectedBuildingPanel;
+class SelectionPanel;
 class BuildButtonBar;
 class BlueprintLibrary;
 class ItemIconCache;
@@ -94,12 +94,11 @@ private:
     std::unique_ptr<ItemIconCache> m_itemIcons;
     GameWorldView*         m_gameWorldView;
     HeaderBar*             m_headerBar;
-    SelectedBuildingPanel* m_selectedBuildingPanel;
+    SelectionPanel*        m_selectionPanel;
     BuildButtonBar*        m_buildButtonBar;
     // The saved blueprints themselves; they have no widget of their own any more and
     // are reached through the two modal dialogs (REQ-UI-BLUEPRINT-DIALOG).
     std::unique_ptr<BlueprintLibrary> m_blueprintLibrary;
-    QWidget*               m_sidePanel;
     ModalDimOverlay*       m_dimOverlay = nullptr;
 
     std::vector<ShipLayoutBlueprint> m_layoutBlueprints;