Updated to webpack 4!

🚀Bring completely new multipage-boilerplate based on webpack 4.

Changes were made:

• Updated to latest webpack 4.x.
• Updated postcss-loader to latest 3.x.
• Updated babel to latest 7.x.
• Replace postcss-next to postcss-preset-env. Postcss-next was deprecated.
• Added postcss-import.
• Removed pug.
• Removed express.
• Added webpack-dev-server.
• Completely re-write build configs.
• Added .editorconfig.
• Added postcss.config.js.
• Added airbnb-base eslint config.