Otherwise the auth/error-handling-interceptor will not kick in.

See: https://dev.to/angular/that-s-why-your-angular-errorinterceptor-may-not-work-5-seconds-fix-52m8

This have to be added be added to other modules as well I guess.

-> compiles but does not work properly

Compodoc is a documentation tool for Angular applications
which generates static html documentation pages.
A documentation of Testcenter Frontend can be build with
```
npm run compodoc
```
I can be viewed under http://127.0.0.1:8080

Make error-handling more consistent and expressive: In case of malformed serverUrl (like with missing trailing slash in docker-network) the error of type DOMException was swallowed completely.

Change routing /priv to /legal-notice

# Conflicts:
#	src/app/maindata.service.ts

Change load message in index.html

Fix lost secondary boxes style (background)

Add a message for the case of files which can not be deleted because they where referenced by others.

A player referenced in a unit can not be deleted without deleting the unit. A Unit used in a booklet can not be deleted without deleting the booklet. A booklet used in a
Testtakers-File can not be deleted without that.

Add Makefile targets for package management

Improve details in README

Remove outdated info from README

One is for retrieving node_modules from container and copy the contents 
into a local directory.
The other is for installing new packages into container. This will 
autmatically be synced to local.