Upgrade AWSSDK to v2

Amazon recently released [v2](https://github.com/aws/aws-sdk-net/releases/tag/2.0.8.2) of the .net SDK. I have done the following:

1. Upgraded the AWSSDK package
2. Using the [v2 migration guide](http://docs.aws.amazon.com/AWSSdkDocsNET/latest/DeveloperGuide/net-dg-migration-guide-v2.html), modified the `ObjectQueue` and `QueueAdmin` classes to fix breaking changes in the API and no longer use deprecated functions