Budget sharing treaty

**What do you want to see?**
A treaty which lets you see your ally's budget, and optionally automatically top up their resources if you have some to spare.

**How would it help players?**
Make alliances more smooth

**Alternatives**
Two separate treaties? But why would you send resources if you don't know that they need them?

**Screenshots and mockups**
N/A

**Things to consider**
N/A