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`
And online doc should point to the different git branches as well ;-)