[IMP] Add region_name, province_code and province_name as usable variables in address_format.
[IMP] PEP8
[REF] _display_address using ADDRESS_FIELDS
[REF] using related field
[FIX] unused import
Merge pull request #1 from eLBati/imp_LeartS_7.0

Refactoring by eLBati: uses related field and doesn't break inheritance.
Merge pull request #13 from LeartS/7.0

[IMP] Add province as usable variables in address_format