Merge branch 'master' into dev

* master: (339 commits)
  Update CHANGELOG.md
  9.0.0
  Update README [ci skip]
  Update CHANGELOG [ci skip]
  npm lockfile
  Update dependencies
  Updated bootstrap to release version 4.0.0 Updated popper.js to version 1.12.9
  Add php-mbstring to list of requirements
  Don't need this any more! :(
  This moves our eslint config in .eslint.js, which allows us to use conditionals in the config file itself, significantly simpliying rule creation. For small-scale differences, this seems to be the simplest solution.
  Rename production eslint file from `.eslintrcProd` to `.eslint.production.json` as per suggestion from @swalkinshaw: roots#2008 (comment)
  Build process now allows console.log, except when the `production` flag is set on `yarn build`, in which case it will throw an error.
  Delete .eslintrc
  Remove some Bower traces
  Update README.md
  Add Code of Conduct [ci skip]
  Change .dev to .test for default local dev TLD per roots/trellis#923
  Bootstrap function in _variables.scss to play nice with other frameworks
  Move variables and Bootstrap imports to autoload
  Remove explicit Bootstrap lines
  ...