Add basic game and possession class

@PragTob Please have a look. This is just the basic setup of the Game and Possession Class. The logic of what kind of possessions have to be generated is still missing and how they are executed. Also the logic how long one possession took. In the future it makes sense that every possession generates its own game log line.

- Created squad factory
- Created a Game class that generates possessions (with `run`) as long as the current game length is lower than 12*4 minutes
- A game has to be initialized with 2 squads
- A possession has to be initialized with `owner_squad` and `opponent_squad`
We wanna do European rules (10 * 60) - manager games are more popular in Europe plus the European league system is closer to what will be built than the NBA one.