Log error stack on bootstrap failure

Log the stack of the error caught during failure to load the web
interface.  This ensure the error is printed to the console instead of
"[fatal] undefined".

packages/web_ui/src/bootstrap.jsx

@@ -72,4 +72,4 @@ async function load() {
 	ReactDOM.render(<App control={control}/>, document.getElementById("root"));
 }
 
-load().catch((err) => logger.fatal(err));
+load().catch((err) => logger.fatal(err.stack));