Add deployment variant for Capistrano

[eoinkelly]

Closes #331

[eoinkelly]

So far we have

1. Generic Capistrano (suitable for deploying to a pet VM we don't manage)
2. Ackama EC2 specific Capistrano (suitable for deploying to the way we like to manage EC2)

I want to explore these options separately because my instinct is that they will diverge quite a lot but if that's wrong, we can look at extracting common code later on.

[eoinkelly]

I'm pretty happy with the generic config now. The Ackama specific variant is currently the same except it adds capistrano-locally but I expect it to diverge as we add the AWS specific stuff

[eoinkelly]

I have extracted the Ackama specific config to a separate PR #350

[G-Rath]

I expect it to diverge as we add the AWS specific stuff

hopefully it shouldn't now 😄 https://github.com/ackama/aws_ec2_environment#with-capistrano