Adding a generic stat model {id, key, title}
Adding a specific stat_data model {stat_id, value, person_id, game_id, event_id, team_id}
- One of person, game, team should be specified
- event is required
- belongs_to person, game, team, event
- Team has_many stats => through stat_data
- Game has_many stats => through stat_data
- Person has_many stats => through stat_data
Fixing through association for event, game, person, team.stats