DataField assumes edited value can be transformed to a suitable String representation

[aalmiray]

DataField<V> assumes that V can be safely transformed to a String literal that makes sense for that particular type, but that's not often the case, specially when dealing with types (domain classes) for which an overridden version of toString() is not available or returns a rather cryptic value.

This design decision imposes a constraint on edited values as it's expected of them to provide a suitable toString() implementation, while at the same time requiring an external transformer (from String to V) by means of FormsFX's ValueTransformer.

It would be much better if JavaFX's StringConverter would be used instead, as it provides both sides of the equation. Retrofitting DataField with StrinfConverter can be done in a compatible way, by deprecating ValueTransformer and redirecting is String -> T transformation to an ad-hoc StringConverter.fromString. Also, a pre-instantiated StringConverter can take care of the default String conversion.

[aalmiray]

Fixed.