DeviceInfo: refactor translation of DeviceInfoPage

- For Boot and Device info widgets, add a retranslateUi() method,
   since the labels change not only in response to translation
   events but also UI events.

FIXES #779

src/modules/partition/gui/BootInfoWidget.h

@@ -30,6 +30,9 @@ class BootInfoWidget : public QWidget
 public:
     explicit BootInfoWidget( QWidget* parent = nullptr );
 
+public slots:
+    void retranslateUi();
+
 private:
     QLabel* m_bootIcon;
     QLabel* m_bootLabel;