[IMP] split state field in two boolean fields with the same feature in b...

with the same feature in base delivery_carrier_label

validated on https://code.launchpad.net/~akretion-team/carriers-deliveries/7-split-default-option-state-from-deliv-method-dbl/+merge/224027

this PR replace the previous closed
Prefer parenthesis over \, and the `or` or `and` operators should be at the end of the line:

``` 
    if (available_option.mandatory or
            available_option.by_default):
        ...
```