Asynchronously require calendar locales

```
These dependencies were not found:

* date-fns in ./node_modules/formol/src/async/CalendarField.jsx, ./node_modules/formol/src/async/CalendarFieldLocales.js
* date-fns/locale/fr in ./node_modules/formol/src/async/CalendarFieldLocales.js

To install them, you can run: npm install --save date-fns date-fns/locale/fr
```

Start with async/CalendarField.jsx and async/CalendarFieldLocales.js, using the reported module-resolution errors as the initial reproduction. Trace how the calendar locales are required and verify the fix by rebuilding or running the project so date-fns and date-fns/locale/fr no longer produce missing-dependency errors.

Written by the indexing model from the issue text.