T53890: Improving static content serving

Static files are now served with an 8-character hash before the last
extension. For example, `tutti.min.js` is now served as
`tutti.min.abcd1234.js`. When doing a request the hash is removed before
serving the static file.

The hash must be 8 characters long, and is taken from STATIC_FILE_HASH.
It is up to the deployment to change this configuration variable
whenever static files change. This forces browsers that download newly
deployed HTML to also refresh the dependencies (most importantly
JS/CSS).

For this to work, the URL must be built with `url_for('static_xxx',
filename='/path/to/file')`. The 'static' module still returns regular,
hashless URLs.

src/templates/nodes/custom/post/view.pug

@@ -21,7 +21,7 @@ meta(property="og:image", content="{{ node.picture.thumbnail('l', api=api) }}")
 
 | {% block css %}
 | {{ super() }}
-link(href="{{ url_for('static_pillar', filename='assets/css/blog.css', v=17320171) }}", rel="stylesheet")
+link(href="{{ url_for('static_pillar', filename='assets/css/blog.css') }}", rel="stylesheet")
 | {% endblock %}
 
 | {% block project_context %}