Removes hardcoded "Misc" settings group translation.

This pull request allows to properly show "Misc" setting group in other languages.

modules/system/classes/SettingsManager.php

@@ -124,7 +124,7 @@ class SettingsManager
          */
         $catItems = [];
         foreach ($this->items as $item) {
-            $category = $item->category ?: 'Misc';
+            $category = $item->category ?: self::CATEGORY_MISC;
             if (!isset($catItems[$category])) {
                 $catItems[$category] = [];
             }