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:
- [ ] Repositoryroot overview
- [x] All bylines
- [ ] Borders around the tabs in tabbedviews
- [x] Document overviews
- [ ] Properties box in document overviews