Implemented workaround for CancellationTokenSource in workflow.

* The problem differed from the earlier incarnations because now the
  workflow itself is being passed between appdomains. This was not good
  because it had a CancellationTokenSource on it that was trying to be
  serialized and this is a no-no (CTS is not serializable). The workaround
  is detailed in the IWorkflow summary.

Signed-off-by: William Raiford <bill.mybiz@gmail.com>