Prepend UTF-8 BOM to csv raw data #162

Fix block-selection in group-monitor: It only registered the click, when the text was clicked, not the whole element.

Fixes https://github.com/iqb-berlin/testcenter-frontend/issues/312

While applying the new linting-rule no-param-reassign, I made a mistake and corrupted the function getNextUnlockedUnitSequerceId (commit #e88e136d). This broke the navigation in some circumstances.

Fixes #https://github.com/iqb-berlin/testcenter-frontend/issues/304

(For some reason) the workspace id is not set yet when entering 
files.component.ts, so by delaying (setTimeout), the workspace id has 
the correct value. Then, the url for file upload is set correctly.

This reverts commit 7288c888.

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Remove outdated info from README