Add support for Ajax requests with X-CSRF header

[odan]

This PR will add support for Ajax requests with X-CSRF http headers.

Currentlythe header names X-CSRF-NAME and X-CSRF-VALUE are fixed and not configurable. If necessary, this could be added later.

Usage

Twig and jQuery

Example:

<script>
    $.ajaxSetup({
        beforeSend: function (xhr) {
            xhr.setRequestHeader("X-CSRF-NAME", "{{ csrf.name }}");
            xhr.setRequestHeader("X-CSRF-VALUE", "{{ csrf.value }}");
        }
    });
</script>