Blob Only Storage Accounts not supported as primary storage account

[mathewc]

They aren't supported as the "primary" storage account (since we need access to queues, etc.). We need to document this, and ideally find a way to throw an error if the wrong type of account is used.

[christopheranderson]

Remaining work: Hide these blob storage accounts in the portal and document that we don't support them.

Closing this issue and tracking work in the docs issue list: Azure/Azure-Functions#38