templates: Use uri_for to reference static paths.

This change is essentially provided by (`**/*.t` is Zsh syntax and something like a `find -name '*.t'`):

```sh
sed -i 's|/static[^"]*|[% c.uri_for("&") %]|;s/\[% size %\]/${size}/' **/*.tt
```

And the reason for this change is to make it easier to change the base path with headers like X-Request-Base to be served within a URI prefix, especially when behind a reverse proxy.