Actor can be run in sync with submisson processing

Description

An actor is designed to be de-coupled/asynchronous to the submission process. It can be run in a separate thread, even after the FormEngine returns the response to the visitor completely. So, there is no guarantee that your modification to a response does not affect the visitor.

By default, an actor is asynchronous. This change provides a new feature for the Actor, so it can be run in sync with the Submission processing, and modify the Response object (to set a cookie, for example).

An actor can only access the Response object if Actor.IsSyncedWithSubmissionProcess is true.