Changed DAO layer (create schema and import SQL)

- Every time the application is ran the database is dropped and
recreated (hbm2ddl.auto=create) and the semantic types are
automatically inserted by loading the semantic_types.sql file.

- The last changes to MysqlMySynsetDAO were undone, since checking for
every synset existence on the DB was to expensive and now unnecessary,
since the schema is being dropped and recreated.

- HibernateUtil now has a method to return Session objects instead of
SessionFactory. The factory does not have to be closed every time,
avoiding multiple loads of hibernate.cfg.xml and multiple schema drops.
Added user confirmation before schema drop

Added a step where the user is asked if he really wishes to run the
application aware that the DB schema will be dropped and all data lost.