Add service to admin

## Concerns
- Service needs be associated to organizations.
- Service need have tags.
- Admins need be able to approve services to be public.

## Todo
- [x] Create service model.
- [x] Create admin for service.
- [x] Create view for showing the service.
- [x] Add state machine. (pending, visible, rejected)
- [x] Add option to reject and approve services on admin.
- [x] Add association to organizations.
- [x] Add image uploader.