Add implementation for Azure Table Storage

[philippgille]

There's another ticket for Azure Cosmos DB: #41.

Azure Cosmos DB offers multiple APIs and because the Table Storage API is advertised as the proper one for key-value pairs, that's what we'll use.

So when implementing a Table Storage client anyway, then maybe let's start with this one and then reuse it in the Cosmos DB implementation.

Also, the "Azure SDK for Go" doesn't seem to have gotten much focus on the Table Storage part and there's no specific client for Cosmos DB, so it should definitely work for Table Storage itself, but maybe there are issues when using it for Cosmos DB.