Added export for csv support

My previous commit in a better organized way - https://github.com/tonytomov/jqGrid/pull/476

I extended the jqGridExport method to allow CSV exporting.

You have 2 extra parameters:

hideColumns: [];
You will use it to choose columns that wont be exported. You have to use colModel.name.

separator: ";";
Choose the separator.

You can use it in this way:

var csv = $("#myGrid").jqGridExport({
                exptype: "csvstring",
                hideColumns: ["Cod"],
                separator: ";"
            });