remove has_many :teams relations from game model
[#72355928] do not allow to add/remove a player to/from a team if the team is playing
remove has_many :players relations from game model
replace POST /games/:id/add_team/:team_id with POST /games/:id/add_home_team and POST /games/:id/add_away_team
[#71700066] create a new game
when creating a new game, home and away team should be different