MAPG-184 measure runtime and show in web output

src/Response/HtmlContent.php

@@ -19,6 +19,8 @@ class HtmlContent extends ContentBase
         $content = ob_get_contents();
         ob_end_clean();
 
+        $content .= '<!-- __debug__runtime: ' . round((hrtime(true) - SCRIPT_STARTED) / 1e+6, 1) . ' -->';
+
         return $content;
     }