Refactor contact selection and implement support for choosing of phone number via contacts

- Removes duplicate contact selection code
- Adds quick a-z scroll position
- Makes adding non-existing contacts more intuitive
- Support choosing of phone number via contacts

Fixes [#5](#5)

![Spacebar_contacts](/uploads/4fcdff6cae6948da7def23fd8bbbfbd2/Spacebar_contacts.png)