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Remove outdated info from README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.

Map sucks

Background for body and secondary boxes

Scaffold edit settings feature in super user; re-arrange appConfig class

resolves https://github.com/iqb-berlin/testcenter-frontend/issues/281