EZP-23437: rewrite rules update for nginx

> Required by [EZP-23437](http://jira.ez.no/browse/EZP-23437) / ezsystems/ezpublish-kernel#1031


Stored images (`var/[dir/]images[-versioned]/*`) are now sent to Sf's `index.php` instead of legacy's `index_cluster.php`
maybe add "on 5.3 or older"

but on the other hand we should not keep versions like this in master, 5.3 stuff should ideally be part of 5.3 release and master should reflect 5.4.

But we need to stop pointing to master rewrite rules from doc to be able to do this, either inline or better by default mention where in your distribution you'll find rewrite rules.