Improve random games

[jensborch]

Games are generated using Go rand.Shuffle, but creating games this way results in many identical games which is not optimal. Games should instead be created by finding all possible combinations of the available players.

The new "shuffle" method should have signature like:

func GameCombinations(players []*model.TournamentPlayer, tables []*model.TournamentTable) []*model.Game {
	var games []*model.Game

        ...	 

	return games
}