add javascript based config file

[kviktorman]

Update back-end URL from environment variables at startup time. With this feature the docker image should not be rebuilt with hardcoded URL before usage. This makes the system more kubernetes deployable.

• add and use startup script for back-end url actualization + nginx start as foreground
• add and import configuration javascript
• replace back-end env url references with back-end url coming from the configuration javascript
• readme update
• sub folder hosting as an environment variable
• login method as an environment variable