[1.x] Adds domain, domain:list and domain:delete aliases

[nunomaduro]

This pull request replaces the terminology of Zone by Domain. In our Vapor Dashboard, we don't see the terminology Zone, and soon, I will pull request a new documentation that will equally not mention the term Zone that may be confusing for some people.

So, now people can use:

vapor domain example.com
vapor domain:list
vapor domain:delete example.com