[WIP] Adds Amazon SNS Support

[Shield1739]

• WIP
  This PR is to adds support for Amazon Simple Notification Service (SNS). Mentioned in the issue SNS topic support for the SQS transport #58

So far my plan is to create a separate transport for SNS instead of adding it to the current SQS support.

So far here are my cons and pros of creating a separate transport:

Pros

• Less abstractions. Some of the code could be reused between the SQS/SNS transports, but due to the AWS SDKs having 2 different packages for SQS and SNS we would need to create some sort of abstraction between the SQS queue and the SNS topic.

If we were to merge it all into the AmazonSqsTransport class, we would need to create a separate field for the Client (IAmazonSQS / IAmazonSimpleNotificationService), Config (AmazonSQSConfig / AmazonSimpleNotificationServiceConfig). The queue/topic creation configuration and attributes would also be different for each endpoint.

• Only load the transport that you are actually going to use. Just because you are using SNS means you are using SQS or vice versa.

Cons

• Harder to integrate the two. SNS and SQS can be used completely independently from each other, but of course the do work well together. Mainly SNS give you the ability to subscribe an SQS queue to a SNS topic, so all messages you send to the topic will be then published to this queue. Automating this setup is something I think we could easily implement from within wolverine. BUT by having 2 different transports it makes it a little more complicated to achieve (at least to my peanut brain).

I had envisioned the ability to create a SNS topic, configure a subscription to a SQS queue and then configure a listener on that same queue all within wolverine. Storing the queues and topics in 2 different transports, just makes this a little more difficult.