So now we test in depth at the model level, and can be a bit more
relaxed about integration tests for translations.
Note we're defining some extra factories to make sure all translatable
attributes with presence validation rules are mandatory. This way we can
simplify the way we obtain required fields, using `required_attribute?`.
Otherwise, fields having an `unless` condition in their presence
validation rules would count as mandatory even when they're not.
Updating it required reorganizing the form so translatable fields are
together.
We also needed to add a `hint` option to the form label and input
methods so the hint wouldn't show up for every language.
Finally, the markdown editor needed to use the same globalize attributes
as inputs, labels and hints, which adds a bit of duplication.
