Add team model
Add Game model. Add teams and some games to seeds.

* Game has three `belongs_to` relationships to Team: home, away, and winner. This allows us to say game.winner, etc.
Remove perf tests
Add IDEA files to .gitignore
Generate Pick model.
Add validations to Game model.

* Teams cannot be the same
Add Pick validations.

* Pick.team must be one of the teams playing in the game.
* User can create a valid pick.
Set up Guard
Add unit test for Team#full_name.
Add more validations to Game and Pick.

* Game: setting result finishes game.
* Pick: finished game requires scores & winner.
Refactor Game "cannot be same team" validation to use :exclusion rather than a custom validator.
Remove unused custom validation from previous commit
Refactor Pick "team must be playing" to use :inclusion rather than custom validation.
Game validation: Team that won must be either home or away.
User cannot bet on the same game twice.
Document issues with uniqueness on Pick model
Game winner must have greater score than loser.
Add winner_score and loser_score to Game
Refactor Game#winner_has_greater_score to use winner_score, loser_score
Implement Pick#decide.

* Rules:
** When wager is 1, and team wins by 1 or more, impact +1.
** When wager is 2, and team wins by 2 or more, impact +2.
** When wager is 1, and team loses, impact -1.
** When wager is 2, and team loses or wins by less than 2, impact -2.