[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
As always with styling, it is a subjective opinion, I find more readable the operator at the end. I consider the operator as the end of the line as a clue for the reader that the code continues below.

Anyway the **most readable** way is the way that is used **consistently**. And since pep8 says `The preferred place to break around a binary operator is after the operator, not before it.`, we should stick to this rule.

I won't block a PR for that though.

> By the way why second is it the preferred one ?

Because pep8 says it. For consistency.