Update: Passing jqXHR for dataSrc in ajax.

There are situations where the data of pagination (total, page, offset, last-page) are sent by headers and other situations where they are sent inside json return. The Datatable only offers me the second option in "dataSrc", so I added support for the this first option.

So I changed the code to include support for jqXHR as second option on dataSrc.