Build system improvements

• use package hawk.javascript from the separate bundle file
• use @codexteam/ajax instead of codex.ajax and codex.transport
• update codex-notifier package
• update @babel's packages
• replace extract-text-webpack-plugin to mini-css-extract-plugin
• add cssnano to minify css bundle
• remove version from package.json
• fix postcss warnings
• fix php notice "... always_populate_raw_post_data ..."
• use Yarn as a package manager: package-lock.json -> yarn.lock
• upload dir was created
• .env file now has correct cache host for docker by default
• a few docs fixes