Added Security Groups

*Please disregard last pull request, made an error on variable names. I changed them from my own configuration to make them more user friendly.


When deploying Amazon Instances, they have to be attributed to a security group. Not many people use the default group since it's a free layer of increased security.

On my own installation of Rex, I have edited the following to include this feature - I think others would benefit from this as well.

Instances listed will now include their security group (for easy on demand grouping) and new Amazon deployments have an additional field (security_group).