[#66731418] when a team gets added to / removed from a game, player_stat for that game should be created / detroyed
refactor player_stat_spec
[#66731780] refactor : change player_stat -> all_time_player_stat / team_stat -> all_time_player_stat
uniqueness validation for team_stat / player_stat
[#66731034] when a player does something, corresponding team/player stat for game should be updated.
refactor game/player