TC-4653 : Add access to iOS App Setting URL

Add access to the iOS8 UIApplicationOpenSettingsURLString. This allows the developer to launch directly into the iOS8 App Settings Screen using Ti.Platform.canOpenURL.

For example:
~~~
var settingsURL = Ti.App.iOS.ApplicationOpenSettingsURL;
if(settingsURL!=undefined){
if(Ti.Platform.canOpenURL(settingsURL))

{ Ti.Platform.openURL(settingsURL);	 }
else

{ alert('cannot open URL'); }

}
~~~