Tpl: add static_root_url() method

src/Tpl.php

@@ -666,6 +666,14 @@ class Tpl {
     return null;
   }
 
+  /**
+   * Get static root URL
+   * @return string|null
+   */
+  public static function static_root_url() {
+    return self :: $static_root_url;
+  }
+
   /**
    * Clean static root URL helper
    * @param string $value