Keyable draw order for C# (pre-Events support)

Notes:
The JSON data loader needs review. This code hasn't caused any problems from my testing though.
Also note that the Apply method in the draw order timeline follows the pre-Events number of parameters. That needs to be changed when Events is implemented.

I'm on the fence about the SetSlotsToSetupPose bug being an actual bug. It's more like a design thing regarding the AnimationState convenience class and the behavior of the Spine objects in each specific runtime using AnimationState.