Enable the ContentObject provider to work with translated referrers

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #54
| License       | MIT
| Doc PR        |

This PR is to make the `ContentObjectProvider` multilang aware. So that when a `ContentObject` provider is used in the chain, and a translated **content** object is persisted, the route provided by the `ContentObject` provider will correspond to locale of the persisted **content** object.

Note that this PR currently only introduces basic support, where by

````
1. Category has auto path `/en/category-1` and `/fr/categorie`
2. Persist article `ceci-est-une-article` with locale `fr`
3. New article will be `/fr/categorie/ceci-est-une-article`
````

However persisting an article in `es` would require persisting a new `AutoRoute` for category with the locale `es`, which I am not sure how best to do.

The default behavior when persisting a content which has a ContentObject provider providing an object not available in the locale of the content should be to take the fallback. This would result in an inaccurate prefix, e.g. `/en/category/ceci-est-une-article-francais` but well, voilà.