Fix various small warnings (#4296)

* Fix `inconsistent-missing-override` warnings

* Fix `final-dtor-non-final-class` warnings

* Fix `ambiguous-reversed-operator` warnings

src/widgets/dialogs/ColorPickerDialog.hpp

@@ -53,8 +53,8 @@ public:
     pajlada::Signals::Signal<QColor> closed;
 
 protected:
-    void closeEvent(QCloseEvent *);
-    void themeChangedEvent();
+    void closeEvent(QCloseEvent *) override;
+    void themeChangedEvent() override;
 
 private:
     struct {

src/widgets/dialogs/EditHotkeyDialog.hpp

@@ -14,7 +14,7 @@ namespace chatterino {
 
 class Hotkey;
 
-class EditHotkeyDialog : public QDialog
+class EditHotkeyDialog final : public QDialog
 {
     Q_OBJECT