I18n support?

Hi,
It seems that there is no [ember-i18n](https://github.com/jamesarosen/ember-i18n) support.
For example, with `columns`:
```js
import { translationMacro as t } from 'ember-i18n';
// ...
columns: computed(function() {
return [{
label: t('agreement.title'),
valuePath: 'metadata.title'
}];
}),
```
`Assertion Failed: Cannot translate agreement.title. <(unknown mixin):ember591> does not have an i18n.`
Is this something on the roadmap or is there another way?

Start with the ember-i18n integration example in issue 311 and reproduce the reported “Cannot translate agreement.title” assertion. Clarify whether ember-i18n support is intended and define the required behavior; completion should resolve the compatibility question with a working approach or a clearly scoped implementation plan.

索引モデルが issue の本文から書いたものです。