Updated vue-vli to version 3, major refactor

frontend/.babelrc

frontend/.browserslistrc

frontend/.editorconfig

frontend/.eslintignore

frontend/.eslintrc.js

frontend/.gitignore

frontend/.postcssrc.js

frontend/README.md

frontend/babel.config.js

frontend/build/build.js

frontend/build/check-versions.js

frontend/build/dev-client.js

frontend/build/dev-server.js

frontend/build/utils.js

frontend/build/vue-loader.conf.js

frontend/build/webpack.base.conf.js

frontend/build/webpack.dev.conf.js

frontend/build/webpack.prod.conf.js

frontend/build/webpack.test.conf.js

frontend/config/dev.env.js