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

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

Now we again have a dev and prod variant and the user needs to run 'make 
init-dev-config'at first time setup.

upgrades eslint ruleset to version 0.0.9 and removes `eslint-disable-next-line no-param-reassign`-exception where it it is possible

load unit fix: request extended by alias to get the correct restore point #261; linting errors ignored!