Pass arguments to AJAX_SUCCESS and AJAX_FAIL

[xfra35]

Usage:

$('#ajax-link').on('modal:ajax:fail',function(event,jqXHR,textStatus,errorThrown){
  //analyze here why ajax failed
});

[xfra35]

:up:

Here's a use case: to give the ability to customize error messages according to the HTTP status (404, 403, 401, 400, 500).

[kylefox]

You're right, this is a good idea — if you're able to get it to merge cleanly I'll be happy to pull it in 👍

[kylefox]

BTW sorry I missed your original PR, not sure how/why I didn't see it!