ui: Move locale and friends into ScreenRecoveryUI class.

Localized texts only make sense on devices with screens.

Test: Run fake OTA on angler; check the on-screen texts.
Change-Id: I3a644294c8b1f2056cfb78b2d61a598b8ddf2acf
diff --git a/screen_ui.h b/screen_ui.h
index 0d7b9e8..eaac2a6 100644
--- a/screen_ui.h
+++ b/screen_ui.h
@@ -191,7 +191,14 @@
   int char_width_;
   int char_height_;
 
+  // The locale that's used to show the rendered texts.
+  std::string locale_;
+  bool rtl_locale_;
+
   pthread_mutex_t updateMutex;
+
+ private:
+  void SetLocale(const std::string&);
 };
 
 #endif  // RECOVERY_UI_H