Support displaying custom validation error messages

[sergei-maertens]

For a number of validation error types (they all have a key in Formio like required, minDate etc.), the form designer can supply there own error message to be displayed. This feature is currently not supported.

Tasks

• For each component type, ensure that we have a type-safe way of accessing the custom error message if provided
• The error messages support some interpolation - figure out how to integrate with react-intl, as i18next has a different interpolation format.
• Ensure that the default validation errors match what is currently defined in Formio/SDK/our backend (see formio/{en,nl}.json in the backend)