introduce a "login" feature

implement an authorization via oic on a /login route

acceptance:

• on a running stand a /login route should be available
• browser should be lead through every openid connect authorization step
• assigned tokens should be displayed at the final page

steps:

• make a research and adopt a db for a session storage
• implement a session object
• introduce a cookie-header as a link to a corresponding session object
• make a research and adopt a oic library for NodeJS
• implement a /login route
• implement a /back_url route
• code necessary token exchanges
• implement refresh_token functionality