Support append to existing blob

> **82e3513** created the issue

After creating an Append Blob on Azure Storage (another way of creating a block blob: https://docs.microsoft.com/en-us/rest/api/storageservices/fileservices/Append-Block ), Cyberduck isn't able to download the file, showing this error:

> Incorrect Blob type, please use the correct Blob type to access a blob on the server. Expected BLOCK_BLOB, actual APPEND_BLOB.