use nunjucks template on browser side

[bmaz]

Warning: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user’s experience. For more help http://xhr.spec.whatwg.org/ Maybe I should use nunjucks.render asynchronously: https://mozilla.github.io/nunjucks/api.html#asynchronous

[boogheta]

Ha I didn't realise your xmlhttprequest was synchronous, async would be better indeed (otherwise it basically freezes your browser during the load)