correctly handle undefined and null attribute values when rendering form fields.
check that serialize correctly handles empty fields.
add locales option to specify which languages to render form in, default to I18n.locale.
use 'label' for label in schema rather than 'title'.
rewording
no need to stub get calls on model, just set values.
check that attribute translations not included in locales array are not rendered in template.
add key value to items returned by getItems() because we need it when rendering template.
assign model schema to return value of view function, accept non-function schema.
call label as a function in template for translated attributes if label is a function.