So now we'll be able to add them to other sections.
We're also adding a `dependent: :destroy` relation to models having
cards since it doesn't make sense to have cards around when their page
has been destroyed.
Not doing so has a few gotchas when working with relations, particularly
with records which are not stored in the database.
I'm excluding the related content file because it's got a very peculiar
relationship with itself: the `has_one :opposite_related_content` has no
inverse; the relation itself is its inverse. It's a false positive since
the inverse condition is true:
```
content.opposite_related_content.opposite_related_content.object_id ==
content.object_id
```
This way we guarantee there will be at least one translation for a model
and we keep compatibility with the rest of the application, which
ideally isn't aware of globalize.
