Update Hibernate mapping files:
- use unique-key instead of unique to avoid unique constraint name generation which can cause problems when updating the database model.
Add schema update strategy for unique constraints. Use RECREATE_QUIETLY instead of default DROP_RECREATE_QUIETLY which cause problems when the SOS tries to remove the old constraints and they do not exist.
Update used DatabaseMetadata constructor. Old constructor is deprecated.
SQL scripts to drop the previously generated unique constraint names.
Reuse the code to identify the database exceptions if the identifier or the observationIdentity (series, phentime, resulttime) already exists in the database.
This was commented out because in the previously used Hibernate version the unique-key definition from the mapping files were ignored.
Merge pull request #72 from CarstenHollmann/feature/define_unique_constraint_names

Define unique constraint names in Hibernate mappings