Implement configurable ajax-timeout/retry/retry-delay for Comet serverpush

The current Comet serverpush implementation uses the default ajax timeout and hardcoded values as a retry count (10), and retry delay(5000ms).

In scenarios where long polling requests are interrupted by a proxy in the middle, it is helpful to customize those settings to avoid the comet functionality from stopping prematurely.
(e.g. with a proxy timeout of 2 mins the comet server push will stop after ~20 mins of inactivity, and critical UI updates might be lost)

see: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/timeout
(NOTE: "In Internet Explorer, the timeout property may be set only after calling the open() method and before calling the send() method.")