Add screwdriver master cli

[dwighthubbard]

It would be useful to provide a CLI for interacting with screwdriver.

I'm thinking it would be useful for the cli to support subcommands with some means of adding
extensions via plugins.

Some things I would like to see the cli be able to do:

• Publish the current Python screwdriver templates to a screwdriver server
• Run any of the existing commands as subcommands, I.E. screwdrivercd check lint could run the same logic as the screwdrivercd_validate_lint command currently does.
• Initial subcommands, I'd like to see:
  • check [validator] - Run a specific validation wrapper.
  • documentation view - Generate and view the documentation.
  • project create [projectname] - Create a new project from the python screwdrivercd cookiecutter template.
  • project update [projectname] - Update the screwdriver.yaml to the version of the templates provided in the the package.
  • repo githook [enable|disable] - Add or remove a githook that runs all validators locally on git commit.
  • screwdriver templatepublish [namespace] - Publish the version of the template in the package to the specified namespace.