Webpack v5 and fix main deprecated: devtool config option changed and now defaults to false

Upgrade deprecated webpack plugins: purgecss-webpack-plugin changed whitelist to better term safelist

Improve and make cache optional on build:

• added build --cache option (allow additional caching time when using it)
• passing --cache option to builders to avoid process.exit and allow cache on idling
• TerserPlugin's new parallel option bug destroy cache on server caching, then disabled (defaults to CPU quantity)

Support webpack 5 error handling: updated webpack compiler error handler to support the v5 stats object