Update packages to resolve dependency conflicts after vulnerabilities.

[hermann77]

After I ran npm audit fix I got package dependency conflicts.
So I installed all the packages in terminal:

npm install @babel/core @babel/plugin-syntax-dynamic-import @babel/preset-env babel-loader babel-preset-minify webpack webpack-cli webpack-dev-server webpack-merge workbox-webpack-plugin clean-webpack-plugin copy-webpack-plugin css-loader html-webpack-plugin mini-css-extract-plugin style-loader --legacy-peer-deps --save-dev

npm install --save lit-element

and

npm install --save @vaadin/vaadin-text-field @vaadin/vaadin-button @vaadin/vaadin-checkbox @vaadin/vaadin-radio-button

The webpack configs had to be updated regarding new APIs (webpack-merge, copy-webpack-plugin).

Please check especially 'from' 'to' options on CopyWebpackPlugin (without flatten option). I'm very new in frontend/JS/webpack etc. :-).

P.S. in package.json I didn't change --env.mode production to --env mode=production yet.

"scripts": {
    "webpack": "webpack",
    "webpack-dev-server": "webpack-dev-server --history-api-fallback",
    "prod": "npm run webpack -- --env.mode production --env.presets serviceworker",
    "dev": "npm run webpack-dev-server -- --env mode=development",
    "dev:sw": "npm run webpack-dev-server -- --env.mode development  --env.presets serviceworker"
  },