Current Time Provider for Timeout Manager

[RobertoDelloglio]

It would be useful to be able to customize the "currentTimeProvider" used by Timeout feature instead of relying on hard coded DateTime.UtcNow.
In this way it would be possible to have full control about the "now" of the system.
This feature could be used for integration test purpose (where we want to test time dependent rules) or to relying on a different time provider other than the local machine time.

[danielmarbach]

@RobertoDelloglio we have plans for the next release after V6 to revamp the timeout infrastructure. We will be considering your simulation needs when we address the timeout manager redesign. Thanks for your input.