For vue-devtools see https://github.com/vuejs/vue-devtools

New linter rules:
* curly
* block-spacing
* keyword-spacing

Also apply all autofixes introduced by these rules

Our linting config in package.json was:
```
    "extends": [
      "plugin:vue/essential",
      "eslint:recommended"
    ],
```

Now switching to "plugin:vue/recommended" and apply all auto-fixes

* add filesize npm package
* add prettyNanoseconds mixin function

New following a different approach to static assets.

See https://www.jerriepelser.com/blog/using-auth0-with-vue-oidc-client-js/
for how to use OIDC client with the npm sources and per-compile updating
the static asset.

Also environment variables now work a bit differently.

Updated README.md accordingly

as vue-resource is retired from official recommendation status
we switch to axios, which is better maintained and supports a
similar API.

for more background see:
https://medium.com/the-vue-point/retiring-vue-resource-871a82880af4