Use one composer.json file

[tobeycodes]

Currently the scaffold ships with 3 composer.json plugins. Some of the reasons why I think this makes sense to use one composer.json

• We are not shipping the theme and plugin to a package repository like packagist.org
• We are loading the same dependencies in multiple composer.json files (vendor bloat)
• We are not truly isolating the theme and plugin. For example we load phpcs at the root, but if we have separate packages each should be responsible for it's own linting
• This will simplify local setup for engineers
• This will reduce build and deploy times in CI
• We can either use move autoloading to a Autoloader class (<20 LOC) or put them at the root composer.json (which forces lazy initialization and good sign of code quality)