Fog jg user unique vote

Fixed opinions so that user can only make one per matchup. Also fixed tests!

![husky_puppy](https://cloud.githubusercontent.com/assets/6283512/4446619/159ac99a-4804-11e4-9882-28b0e62e7259.jpg)

Nice custom method!  I'd modify this to take an actual `matchup` object rather than the ID.  Also use parentheses for arguments:

```ruby
  def has_opinion?(matchup)
    if opinions.find_by(matchup_id: matchup.id)
      return true
    end
  end
```