Limit number of players in a game

[robert-damoc]

Add a limit to the number of players that can be in a game. I suppose the limit should be 8.

1. Add a constant in the games model, with the proper value
2. When you add players to a game, make sure that the limit isn't reached
3. In the Games List (#index), add a new, sortable column, that shows how many players out of how many are there (e.g. 5/8)

[MariusTulbure]

this issue was included in the previous 2 isuses that i had, and it's now resolved