Fix changing focus around the main window using tab

* Override Qt's default [broken] behavior of handling Tab/Shift+Tab to navigate around the MainWindow. Completely fixes trapped focus.

* Improve handling of search results when navigating the UI.

* Fix selecting first entry after ending a search.

* Add keyboard shortcuts to directly focus on search (F1), Group List (F2), and Entry List (F3)

* Fixes #2878, #4636, and #4221

src/gui/MainWindow.h

@@ -85,6 +85,7 @@ public slots:
 protected:
     void closeEvent(QCloseEvent* event) override;
     void changeEvent(QEvent* event) override;
+    bool focusNextPrevChild(bool next) override;
 
 private slots:
     void setMenuActionState(DatabaseWidget::Mode mode = DatabaseWidget::Mode::None);