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

Bumps [hosted-git-info](https://github.com/npm/hosted-git-info) from 2.8.8 to 2.8.9.
- [Release notes](https://github.com/npm/hosted-git-info/releases)
- [Changelog](https://github.com/npm/hosted-git-info/blob/v2.8.9/CHANGELOG.md)
- [Commits](https://github.com/npm/hosted-git-info/compare/v2.8.8...v2.8.9

)

Signed-off-by: dependabot[bot] <support@github.com>

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 latest image is not actually used anywhere so can be removed for 
now. The tagged image process was faulty. This makes it so, that the 
tagged build is only run on special tag CI-runs.

This is only used within the build so can be discarded soon after.