- added charset param in database import command
- moved PostgresConfig to sekai-db proj
- added dependency gson
- added data_tool/sekai_master_db with a Music which can parse sekai-master-db musics.json and convert it to the Song object
- 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)