...rather than embedding them into index.html.
This is only acceptable for dev, but the next commit adds an alternative
mechanism for prod.
There isn't actually a manual deployment step here. However, this commit won't
work on staging / prod without the next one (since we don't serve
zephyr/static/templates in prod).
(imported from commit dce7ddfe89e07afc3a96699bb972fd124335aa05)
