Map sucks

Background for body and secondary boxes

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

The API will send the appConfig as key value pairing, so we need some transform procedures. The getAppConfig function prepares for super user setting edit.

Move warning from card-header to alert tag; remove workaround via customTexts (system_announcement)

Application data on impressum page only

Logo flexible; move some main.dataservice infos into appConfig; new appConfig data: html, warning etc.

by giving systemAnnouncement a starting value

The old one was result of experimentation. The backend address should be 
/api so it works out of the box.

resolves https://github.com/iqb-berlin/testcenter-frontend/issues/247

closes https://github.com/iqb-berlin/testcenter-frontend/issues/282

The mock is nw the default, the old dev file was of no use outside the 
setup project, so it is kept there now.

The backend address in the environment file needs to either be localhost 
for using the app from the (host system's) browser of the internal 
docker name (backend-mock) so the frontend container can reach it. SO 
the testcenterUrl can either be reached from the host or fromt he 
frontend container but not both. This makes it so, that the e2e tests 
use a specific environment (defined in angular.json) which uses a 
different environment file for running e2e test within the frontend 
container.

instad the internal one

restores the version of notifyDyingTest with employs the specialized endpoint and the fetch-api als alternative to sendBeacon. It was appareantly lost my merging with master.

No Changes in the behaviour.