Styling improvements needed for the opengever.core styling rebuild

Because of the integration of plonetheme.teamraum in to opengever.core the html-structure of some templates has changed. Therefore some styling improvements in the izug.basetheme are necessary:
- [x] Repositoryroot overview
- [x] All bylines
- [ ] Borders around the tabs in dossier tabbedview
- [x] Document overviews
- [x] Properties box in task overviews