[WF4] Tidy up tabs. BookmarkOptions validation. Small refactor.

-Changed spaces to tabs
-ScheduleHostBookmarkResumption now calls ResumeBookmark as there was
dupe code.
-Few test changes.
[WF4] Scheduling Activities with FaultCallback support and tests.

-Also
 -Changed ActivityInstance.IsCompleted to calculate return value based on
  current ActivityInstanceState
 -Removed NativeCallbackActivityContext as it wasn't providing correct
  validation in any form. Callback delegates need validated to ensure any
  anon methods passed do not close variables. Param access is permitted,
  which is the only thing this class stopped
 -Split test files / classes.
 -WorkflowRuntime now swallows all exceptions, changed WorkflowInvoker
  to implement unhandled exceptions event and re-throw them