Update Webapp dependencies

[roscisz]

Webpack v3 has vulnerabilities, but upgrading requires in build_vue/webpack.prod.conf.js:

• uglifyjs-webpack-plugin is deprecated
• extract-text-webpack-plugin is deprecated
• CommonsChunkPlugin has been removed, proper optimization and optimization.minimization configurations have to be developed and tested
• maybe more?

dart sass seems to be preferred over node-sass