Enable CORS support in FormManager

The FormManager JavaScript class is used to submit & validate forms via AJAX without full page reload. However in case, when we're located in a non-secure page (on http:// url) and want to AJAX-submit form to secure page (on https://) we're getting CORS error, because to JavaScript change in protocol is already considered as cross-domain request.

To avoid this we need to:

1. set crossDomain: false in the options of any ajax request that FormManager does
2. just send headers below and exit in case if $_SERVER['REQUEST_METHOD'] == 'OPTIONS'
3. send following headers before outputting content to a browser:

header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Headers: X-Requested-With, Content-Type');

We have 2 problems with header sending:

1. if we send them in kApplication:Done method, then the events, that don't parse template won't get them
2. if we send them in event processing code then with no event in url the template won't get them
3. if we set in both places then we get double amount of headers when both template & event are present

What we miss in the application is the ability for centrally specify what headers needs to be sent (possible with override from event/template) before content is displayed.

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