Move Provision 4.x branch to GitHub in it's own Organization

Hi there.

A few weeks ago, I emailed the core maintainers of Aegir to propose a future path for Provision.

The new 4.x branch is shaping up to be a great CLI tool in it's own right.

I proposed to Provision4 should be removed from the "Aegir" organization and released into the wild as a standalone organization to support the main app: The Provision4 CLI.

The team was very supportive. Here are the steps I've taken so far:

1. Create a new GitHub organization: https://github.com/provision4
2. Push the 4.x branch (and some open PRs) to the new repository: https://github.com/provision4/provision
3. Created a new Twitter account: https://twitter.com/provisionCLI
4. Bought new domains (for 5 years!): provision4.com provision4.org
5. Created a new GitBook documentation page: https://docs.provision4.org/
6. Blogged about it: http://www.thinkdrop.net/announcing-provision-4-leaving-aegir-nest

Here are some things I have yet to do:

1. Delete the 4.x and related branches on drupal.org
2. Change the Aegir\Provision PHP namespace.
3. Find any other remaining mentions of "aegir" and mitigate them.
4. Recruit the 4.x development team!!

We plan on figuring out a way to let Aegir 3 use Provision 4 as a back-end instead of drush+provision3.x. We've already taken a number of steps to make this happen like #2957156: Convert Provision to include ClassLoader using composer.json and autoloader.php.