Dependency updates

[ghost]

Summary: Dependency updates to fix yarn audit issues. Still requires some testing, and maybe the upgrading of webpack itself.

Discussion points:

• webpack-merge introduces a dependency on node >= 8.9 Is this a problem on production systems?
• should we upgrade webpack itself? This comes with a rewrite of some webpack config, and potential new dependency problems

What the PR currently does:

• modernizing some dependencies, bringing down the yarn audit to 1 low priority issue. Major changes in dependencies are:
  • using package open instead of opn
  • removed unused tests and test frameworks
  • removed some unused packages
  • due to webpack-merge update the minimal node version jumps to 8.9 (only for development, production should still run fine on older node versions)

[bernhardreiter]

webpack-merge introduces a dependency on node >= 8.9 Is this a problem on production systems?

No, as this is just a build dependency (AFAIU) and there is no javascript engine deployed on production servers, the production build yarn build is only delivered to front end webbrowsers (which of course do not run nodejs. :) )

[bernhardreiter]

Merged after some testing. Thanks!