- change the id and seq and name def of SongUnit
- change and added fields to Song
- change and added fields to Difficulty
- add subproj sekai-database for db connection and action(empty currently)
- add sekai-cli command database to execute database manager action(no implementation currently)
- changed the target database from mysql to postgresql
- so the db.table_prefix changed to db.struct.
- added getAll on Difficulties type
- renamed sekai-scores-db to sekai-meta
- add a new resource file, it will be the next song data storage method.