Feat: Add CustomReward

[Mangochicken13]

• Adds abstract class CustomReward;
• Patches Reward.FromSerializable to check for custom rewards first
• Patches RewardSynchronizer to handle custom rewards and associated messages
  • Adds abstract class CustomMessage
  • Adds struct CustomBufferedMessage
  • Adds TransformCard reward
  • Adds TransformAndUpgradeCard reward
    • These currently do not have a prefix to the LocString's associated, need to look into that as well

[Mangochicken13]

Rebased onto develop & changed merge target