1) Implemented a generic CodeImporter, importing code labels from an
xls, and generating a file containing the definition of Java constants;
2) Added new Code subclasses related to activity sectors
(PublicPrivateCode, ActivitySectorCode), and NACE (Nace1Code, Nace2Code,
Nace3Code);
3) Cleaned AwacDummyDataCreator: removed useless test data (from
previous phase of development), removed code labels insertions (those
are now imported by CodeImporter);
4) Other minor improvements.