Feature Request: Public API for getDescriptionFor

In my app, the propertyName for the input does not always map to the displayed label; this would be even more common in localised products.

For example:

```
{{spanishProperty}}

{{#if (get changeset.error property)}}

{{#each (get (get changeset.error property) "validation") as |message|}}

• {{message}}

{{/each}}

While it is possible to change the messages hash per language, the hardcoded `{description}` just takes the propertyName and normalises it.

Would it be possible to allow the `app/utils/messages.js` file to be overridden, in order to allow more complex names for the `{description}` placeholder?