Include leaderboard scores in unlocks API

[Jamiras]

As a player, I'd like to know my previous best score when starting a leaderboard attempt.

This information is not currently available to the toolkit. Recommend adding it to the unlocks response. Current response:

{
  "Success":true,
  "UserUnlocks":[2286,4135,4136,4137,4138,4140,4141,4153,4154,4156,4159,
                 4160,4161,4165,4167,4168,4172,4173,4192,4193,4194,4195,
                 4196,4197,4198,4199,4201,4312,4313,4314],
  "GameID":232,
  "HardcoreMode":true
}

Recommend adding a "Leaderboards" array with elements similar to this:

"Leaderboards":[{"LeaderboardID":19,"Score":7430,"DateSubmitted":1549686087,"UserRank":"111"}, ...]

The leaderboard ID and score are the most important. The UserRank could be leveraged for showing a change in rank when submitting a new score.

Leaderboards where the player does not have a current entry should be excluded.