- Changed the Fields. Fields are now inherited from a generic type Field
that defines a field name and its annotation.
- Changed everything to use only one collection of fields (there are no
more mandatory and optional fields, but just fields that should be
instantiated).
- Inserted topNodes.xml as a kind of template for preferences. This file
includes all the top nodes that should be considered for the preferences
statements (the format can eventually be updated if needed).