This is a prerequisite for supporting skinning of leaderboards.
- New `IGameplayLeaderboardProvider` and `IGameplayLeaderboardScore`
interfaces are introduced. They are strictly concerned with supplying
leaderboard data.
- Logic of managing display, which was previously jammed into the
inheritance hierarchy of `GameplayLeaderboard`, is now moved into
`IGameplayLeaderboardProvider` implementations. Solo play,
multiplayer, and multiplayer spectator get their own implementation of
the interface.
- The inheritance hierarchy of `GameplayLeaderboard` and per-player
overriding of the implementation of the gameplay leaderboard is gone.
Only one drawable class (renamed to `DrawableGameplayLeaderboard`) is
allowed to display the leaderboards, across all modes of play.
Bartłomiej Dach