Update AzureReader2 to fix one small bug and improve performance.

* Minimize number of calls to Microsoft Azure Blob Storage for existence
checks.
* Makes as many variables private/internal as possible.
* Automatically derive storage endpoint from connection string if none
is provided.
* Make properties auto properties where appropriate.
* More comments.

I hope that I have kept your coding style well enough. I am used to different (ReSharper) style :)