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

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