Add a CLI
It'd be handy for testing (among other things) to have a CLI for Aegir5. I think we should be able to use Drupal Console to auto-generate command options based on entity bundles, etc.
- basic CRUD for aegir entities (platforms, sites, operations, tasks..)
- auto-computed fields/options, so we can prompt for them dynamically
- extend to allow running operations/tasks directly from CLI