105 integrate authorization code flow into readerbench vue

[ManuTrt]

• Integrated Authorization Code grant type (https://developer.okta.com/blog/2018/04/10/oauth-authorization-code-grant-type).
• Use env files for reading api urls and other global public values
• To maintain a better separation of concerns and extendibility Login and Register are fully managed by the Authentication Server (Readerbench API).
• Short flow explanation: The Client (Readerbench Vue) will ask the Authorization Server (Readerbench API) to access the Resource Owner's (User) data (models, datasets etc.) on their behalf from the Resource Server (Readerbench API). The User has to be authenticated (a session must exist). The Client gets a code that will use to get an access and refresh token.
• Update: Added PKCE extension

Closes #105