[WF4] Emulate .NET handling of anon methods used as CompletionCallback

-Preliminary work for simplification of Variable/Argument initialization
by Expression Activities
[WF4] Simplification of initialization of variables and arguments

-New solution is much cleaner utilising Schedule Activity with callback
feature of runtime
-Cleans up :
  -Task handling: no longer a concept of an initialization task
  -Argument handling: no longer special handling for "Result" arg of
   activities passed in initialzation tasks
  -l value handling: no longer temporary storage of references retrieved
   and the need to call HandleReferences before execution of activities