Use Yarn Workspaces

[hawkrives]

• makes use of Yarn's workspaces feature to allow the individual packages to declare what they depend on
  • this lets me move things that the CLI's need out of the giant list of things in the top-level package
  • it does mean that Greenkeeper's going to not be as helpful, since it'll only see the top-level updates, but at this stage in Gobbldygook's life I'm OK with that
• Switches out the spinner for one of the https://kyleamathews.github.io/react-spinkit/ spinners
• Moves the HTML plugin for web pack into its own module
• Documents explicit interdependencies between modules