A large PR

- added general GitHub OAuth implementation (including a new entity to store the OAuth credentials.
- added an automated process to generate zikula.manifest.json and composer.json files for new repositories as well as setting up the webhook properly.
- improved webhook responses.
- added a news_id field to the CoreRelease entity (not used yet) to link to the corresponding news comments in future.
`readfile` cannot be used here as it sends headers to early.