optimization - fixes too many queries

DO NOT MERGE UNTIL WE ARE READY TO TAKE NON-CRITICAL CHANGES

Since this partial is rendered on the signup page and the prizes page, it seemed worthwhile to go back and fix this code.

new code generates this:
   (39.3ms)  SELECT COUNT(*) AS count_all, prize_provider_id AS prize_provider_id FROM `prizes` WHERE `prizes`.`user_id` IS NULL GROUP BY prize_provider_id
  PrizeProvider Load (0.4ms)  SELECT `prize_providers`.* FROM `prize_providers` WHERE `prize_providers`.`id` IN (1, 2, 3, 4, 5, 6, 7, 10)

old code generated this:
  PrizeProvider Load (0.4ms)  SELECT `prize_providers`.* FROM `prize_providers`
   (11.0ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 1 AND `prizes`.`user_id` IS NULL
provider
   (0.5ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 2 AND `prizes`.`user_id` IS NULL
provider
   (8.7ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 3 AND `prizes`.`user_id` IS NULL
provider
   (7.5ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 4 AND `prizes`.`user_id` IS NULL
provider
   (9.2ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 5 AND `prizes`.`user_id` IS NULL
provider
   (12.7ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 6 AND `prizes`.`user_id` IS NULL
provider
   (11.4ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 7 AND `prizes`.`user_id` IS NULL
provider
   (0.4ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 8 AND `prizes`.`user_id` IS NULL
   (0.3ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 9 AND `prizes`.`user_id` IS NULL
   (7.0ms)  SELECT COUNT(*) FROM `prizes` WHERE `prizes`.`prize_provider_id` = 10 AND `prizes`.`user_id` IS NULL
provider