add :id to permitted params for nested attributes

fixes https://github.com/spree/spree_i18n/issues/312
Idea comes from: http://stackoverflow.com/questions/17515672/strong-parameters-for-nested-attributes-returns-unpermitted-parameters-when-em

This is fixing the problem but there are two omissions:

- a proper spec
- a look into the other controller decorators, the problem is probably existent there, too

I could really need help regarding the spec.