Use space character as a separator for event names in AjaxEventBehavior

At the moment AjaxEventBehavior uses "\s+" regex to split the string with event names.
This splits by one or many space(s), tab(s), vertical tab(s), carriage return(s), ...
But there is no need of the extra complexity. We should use only space character as a separator. This is what users use anyway. And it is better performant.