The submitted button value is only required when pjaxing a form, right? Noone would expect it when using pjax on a link, wouldn't they?

So, adjust `handleSubmit` and pass the value of a submit button if one was clicked and otherwise submit the value of the fist submit button of the form, in case it was submitted using ENTER key.

You also won't need this hidden field and instead pass the value alongside other data using jquery's ajax() with the data option...