Treasury burning can be directed (#6671)

* Treasury burning can be directed

Also, Society is a imbalance handler

* Build

* Introduce from_permill in perthings.

* Rename to from_perthousand to avoid confusion with Permill

* Fixes

substrate/frame/treasury/src/tests.rs

@@ -149,6 +149,7 @@ impl Trait for Test {
 	type ProposalBondMinimum = ProposalBondMinimum;
 	type SpendPeriod = SpendPeriod;
 	type Burn = Burn;
+	type BurnDestination = ();  // Just gets burned.
 	type WeightInfo = ();
 }
 type System = frame_system::Module<Test>;