Allow to send extra parameters in the POST request.

[AlbertoNieto44]

trafficstars

It would be good to be able to extend the data which is sent through the ajax requests.

As as example, let us imagine that we want to update several records at once in a tree view. Then we would need the selected elements to apply the changes. Like this:

It would be good to add an extra option in the settings dict to make it extendable.