Update BlobErrorLog.cs

* Make work with Azure Storage 2.0.
* Blob name now also error id.
* Blob list pre-sorted, with newest first.
* GetError can now call for direct blob, instead of first getting list.
* No additional call needed, in loop of list, as casting blob as appropriate type.
* Substantial decrease in Azure transactions, due to more targeted calls.
* Blob container no longer public, by default (this security hole allowed anonymous browsing of error information).