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

Notes:
The JSON data loader needs review. Then maybe the comments can be removed. It 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.