respect users timezone in statistic widgets (#1207)

src/Entity/User.php

@@ -256,14 +256,16 @@ class User extends BaseUser implements UserInterface
         return null;
     }
 
-    /**
-     * @return string
-     */
     public function getLocale(): string
     {
         return $this->getPreferenceValue(UserPreference::LOCALE, User::DEFAULT_LANGUAGE);
     }
 
+    public function getTimezone(): string
+    {
+        return $this->getPreferenceValue(UserPreference::TIMEZONE, date_default_timezone_get());
+    }
+
     /**
      * @param string $name
      * @param mixed $default