3.11.17

Fix: skip empty email requests.
Fix: prevent double check request.
Fix: update cron class.
Update version. Add site exclusions.
Fix: set OnEndBufferContentHandler and OnPageStartHandler static.
Fix: rc_check type.
Upd: set url exclusion textarea. Disable module for excluded urls.
Fix: added isset in /Common/Helper.php in http__get_headers()