Update and prune dependencies in Lumino 2

[afshin]

We should audit the dependencies and devDependencies of the packages (and the meta-package) and make sure they are up to date. We have a lot of warnings in the build logs and console output and we are using outdated versions of tools like ESLint, among others.

Relevant issues and PRs

• Lumino 2 - meta PR with multiple items resolved #319
• Update devDependencies, fix eslint, use ES6 #330
• Remove webpack from Lumino examples and code base #332
• Remove some webpack artifacts from devDependencies #396

[fcollonval]

As commented in #330, it will be nice to drop webpack and to use rollup for the tests to remove any inconsistency between the packager used for publishing and for testing.

[blink1073]

The only remaining warning is:

warning "@jupyterlab/buildutils > verdaccio > clipanion@3.1.0" has unmet peer dependency "typanion@*".

I'm closing this one as complete.