GitLab

* 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