Windows 8 Storage fixes

* Fixed BeginShowSelector / EndShowSelector not working.
* Fixed BeginOpenContainer / EndOpenContainer not working.
** Static variables added as a workaround for not being able to cast IAsyncResult to AsyncResult.

* Fixed StorageContainer methods throwing exceptions because there was no wait on the async methods.
* Fixed base path for StorageContainer
* Added a try/catch to StorageContainer.FileExists and StorageContainer.DirectoryExists
* Fixed OpenFile opening a Stream on the end of the file when the file existed.