Ask google not to translate the page

We already have i18n. Furthermore, Google may analyse sensitive content for
the purpose of recognising whether the page needs to be translated, see
https://support.google.com/webmasters/answer/79812?hl=en

Ref https://github.com/threema-ch/threema-web/pull/681

tpl/bootstrap.php

@@ -11,6 +11,7 @@ $isPage = substr($template, -5) === '-page';
 		<meta name="viewport" content="width=device-width, initial-scale=1">
 		<meta name="robots" content="noindex" />
 		<meta name="referrer" content="no-referrer">
+		<meta name="google" content="notranslate">
 		<title><?php echo I18n::_($NAME); ?></title>
 <?php
 if (!$isDark):