State of cross server support

[SOF3]

Tracking issue for supporting multi-server economies:

• Use a shared database like MySQL
• addMoney and reduceMoney should be atomic
• Transactions should be atomic: The money deduction operation and the balance checking should be performed and checked together. https://github.com/ParoxityTeam/ParoxityEcon/blob/c38371cfb6af397aa097a7ecf8cc37a1c0906ce4/src/Paroxity/ParoxityEcon/ParoxityEconAPI.php#L187-L191
• Gameplay configuration across servers might need to be synchronized (when currencies are introduced, otherwise some currencies only existing on particular servers would crash other servers). See ModernEconomy for an example of how to do this.