Use the boolean fields instead of the state field

Following https://github.com/OCA/carrier-delivery/commit/59038bd27aee9a7f8b65740103bfa1826e62a6da,
the 'state' field has been replaced by boolean fields.

Closes #43
Merge pull request #44 from guewen/7.0-postlogistics-state-issue43

Use the boolean fields instead of the state field