Update bootbox.js

Added Ajax Functionality to the Dialog function by passing URL, Also add two events onLoad,onAjaxLoaded
ex:
bootbox.dialog({
          url:"test.php",
          message: "-",
          title: "Title",
          onEscape: function() {},
          show: true,
          backdrop: true,
          closeButton: true,
          animate: true,
          className: "my-modal",
          onLoad:function( d ) {
               // Event triggered when model is shown
          },
          onAjaxLoaded:function(d){
                //Event triggered when ajax request is finished
          }
});