CON-1296 | ABTesting uses nocookie domain for external scripts

https://wikia-inc.atlassian.net/browse/CON-1296

New variable was introduced on frontend and in PHP: 
```
window.wgCdnApiUrl and $wgCdnApiUrl
```
Api url on cookieless domain is stored there. For production current value is: 
```
http://api.wikia.nocookie.net/__cb{cacheBuste value}
```

In addition PHP methods for getting API urls were updated:
* ````ControllerName::getUrl( $method, $params = null, $format = null )```` stays without changes - this is alias for ````ControllerName::getFullUrl( $method, $params = null, $format = null )````
* ````ControllerName::getFullUrl( $method, $params = null, $format = null )```` - returns full URL for API method on current wiki
* ````ControllerName::getLocalUrl( $method, $params = null, $format = null )```` - returns local URL for API method 
* ````ControllerName::getNoCookieUrl( $method, $params = null, $format = null )```` - returns URL for API method using cookieless domain

Similar work was done on frontend. From now ````$.nirvana.sendRequest()```` uses ````$.nirvana.getUrl()```` for URL calculation.
```
		/**
		 * Get Nirvana API url
		 *
		 * @param Object options
		 *  controller - controller name
		 *  method - method name
		 *  format - (optional) responce format
		 *  scriptPath - (optional) url protocol and location
		 *  data - (optional) additional query string params
		 * @returns {string}
		 */
		function getUrl( options )
```

**Don't merge without https://github.com/Wikia/config/pull/512.**
I wonder if this is the optimal place to define allowed formats. 
What do you think about keeping a list of those formats defined at the beginning of nirvana scope?