ARQGRA-86: XHRHalter renamed to AjaxHalter

- renamed all dependent classes, .js files, method names, etc.
- AjaxState moved to API module
ARQGRA-86: AjaxState moved to halter api package
ARQGRA-86: Fixed manipulation of XHR objects properties

- some of the XHR object properties, like status, statusText, reponseText, responseXML can be accessed only after readystatechange == 4
- fixing this enable to use alos phantomjs with AjaxHalter
- when XHR object is in different state, those attributes are filled with default values accordinf to spec.: http://www.w3.org/TR/XMLHttpRequest2