Feature/change game tournament structure

Changed so the following API endpoints accept <code> tournament </code> slug
     /games
     /latest_news
     /featured_matches
     /carousel

Also changed so we are accessing only active tournaments
`tournament.status in ('A', 'S')` possibly. Might be worth to put something like `ACTIVE_TOURNAMENT_STATUSES = ('A', 'S')` in a constants.py somewhere. Just something for later.