[WIP] Adminpanel

so far
- [x] add .admin method to Person model
- [x] make a dashboard index view that displays the current admins
- [x] make changes to the user menu, so that admins can access the dashboard

next steps
- [ ] possibility to make and unmake admins from the dashboard and the person views
- [ ] possibility to delete groups and users from the dashboard and the corresponding views
- [ ] blog administration
- [ ] add random gif

questions:
what tests do I need? and *where* do I need to put them?
This could be done in one link_to line as well.