Idea: sopel-plugins new CLI

[dgw]

It's possible to invoke cookiecutter programmatically, meaning we could have a CLI command shipped with the bot that starts generating a new plugin. Couple preliminary details:

• sopel-plugins new is just my initial thought. Could be called something else, or live in a different namespace (e.g. separate this and any future developer-oriented commands into a sopel-dev CLI)
• While Sopel could just auto-install cookiecutter as a dependency, alternatively, this can be an optional feature:

  try:
      from cookiecutter.main import cookiecutter
  except ImportError:
      print("To use this feature, install the `cookiecutter` package and try again")

(This random idea brought to you by streamlining the name of our cookiecutter template repo.)