AI-499 :

 - unit is shown only for QUANTITY field type;
 - added convertable types to FormFieldType e.g. QUANTITY  -> NARRATIVE, FREE_TEXT
 - On "Change" type button only convertable types are shown (if user wants inconsistent behavior he/she can always add new field). It's not possible to change REFERENCE type
 - Added ChangeTypeDialog and FormFieldTypeCombobox widgets.
 - label, description, unit is editable -> reflected by ui
 - type dynamic widget regeneration is added.