Add worker task post processing options

* RepeatingWorkerTask implementations can now pass back an override
custom delay duration from each processing iteration
* CloudQueueWorkerRoleTask implementations can now pass back a custom
delay after each iteration
* No broken public interfaces, only additions.  You can still leverage
the old method overloads, or you can switch to the new ones to leverage
the new capability.  Behavior should still be the same if new options
are not leveraged.