AUI-1536 Remove createField from the property-builder-field-support augmentable class

once now we use it by augmentation, instead of by extending it. This class must be implemented by any class that augments it.

Signed-off-by: Henrique Vicente <henriquevicente@gmail.com>
AUI-1536 Add example of nested field in the FormBuilder demo

Signed-off-by: Henrique Vicente <henriquevicente@gmail.com>