Replace CoffeeNet OAuth2 with OpenID Connect

[punycode]

CoffeeNet authentication & authorization is currently based on a custom protocol on top of OAuth2. Moving forward, we want to replace this implementation with a standards based one, namely one based on OpenID Connect. This will allow a wider range of authentication sources, like Google, GitHub, Auth0 or Keycloak.

• [x] Create auto-configuration for popular OIDC providers
  • [x] Remove dependency on a particular OAuth2/OIDC implementation from core CoffeeNet classes
  • [x] Still support a development mode authentication scheme for easy hacking on CoffeeNet applications

[punycode]

While working on the #68 PR it became apparent, that trying to force the previous notions of a global CoffeeNet administrator role into the framework is counter-intuitive, since this is deeply dependent on the actual applications built with the framework.

I therefore removed that checkbox from the list above.

[punycode]

Sunsetting coffenet-auth is actually not really tied to this issue, so I removed it and will now close this issue.