[FEATURE] improvements of contact import

__Tasks:__

- [x] more abstractions in import;
- [ ] better (more general) handling of relations like email,..
- [ ] gather feedback for my changes 

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | [none]
| Doc           | none