#152 Removed CslaTaskFactory from Csla.WinRT assembly

There is just so few options for scheduling async tasks on WinRT and very little to be done by methods exposed on the TreadPool. 
http://msdn.microsoft.com/en-us/library/windows/apps/windows.system.threading.threadpool.runasync.aspx 

The ThreadPool in WinRT only exposes 3 awaitable methods and is quite limited.

Also some interesting observations here:
http://social.msdn.microsoft.com/Forums/windowsapps/en-US/2a337af3-23ed-4252-b05f-a15e525d365f/winrt-task-scheduler-unfairness 

closes #152