[FIX] delivery: Delivery methods not translated

In function name_get on model "delivery.carrier", the field name
is taken from "product.template" and the translations were just
available on model "product.product".

The translations for the "product.template" records were not available
in the .pot file because there was no external identifiers created for
the "product.template".

Now when creating the external identifier of a record, all the external
identifiers of the inherits models of this record are also created.
In this way, all the translations will be created.

opw:728682