Drop contact info utility

I replaced all `IContactInformation` methods with the direct use of the `ogds_service` or some separate helper objects like the `ContactService` or  the `SortHelper` objects.

Fixes #362.

@deiferni 
@phgross  I propose to add a `contact_service` helper function to access the service instance. That way using the contact service looks the same as `ogds_service`, i.e.:
```
from opengever.contact import contact_service
contact_service().peter()
```