Bug 885546 - VCF importer saves type="UTF-8" in contact fields [r=arcturus]

This Pull Request does the following things:

- Assign proper type to multi-property fields (thus solving the UTF-8) bug
- Assign proper "PREF" property to `mozContact` if present
- Simplify and optimize parts of the code
- Fix regression introduced by referring to `navigator.mozContact` instead of just `mozContact`.

Thanks again, @arcturus!