The Kentucky Derby is still more than a month away, but Churchill Downs Inc. executives are already celebrating a big payday. A lot of money passes through CDI. The Louisville-based gaming company owns five horse race tracks, six casinos and the nation’s top online wagering site, TwinSpires.com. Last year it took in $2.5 billion in bets, which led to $779 million in revenue and an 11 percent gain in the measure of profit used to calculate executive bonuses. Shareholders loved it, driving up the stock price by 35 percent last year, to $89.65.