Per-things trait. (#4904)

* Give perthigns the trait it always deserved.

* Make staking and phragmen work with the new generic per_thing

* Make everything work together 🔨

* a bit of cleanup

* Clean usage

* Bump.

* Fix name

* fix grumbles

* hopefully fix the ui test

* Some grumbles

* revamp traits again

* Better naming again.

substrate/frame/timestamp/src/lib.rs

@@ -99,7 +99,7 @@ use frame_support::traits::{Time, Get};
 use sp_runtime::{
 	RuntimeString,
 	traits::{
-		SimpleArithmetic, Zero, SaturatedConversion, Scale
+		AtLeast32Bit, Zero, SaturatedConversion, Scale
 	}
 };
 use frame_support::weights::SimpleDispatchInfo;
@@ -112,7 +112,7 @@ use sp_timestamp::{
 /// The module configuration trait
 pub trait Trait: frame_system::Trait {
 	/// Type used for expressing timestamp.
-	type Moment: Parameter + Default + SimpleArithmetic
+	type Moment: Parameter + Default + AtLeast32Bit
 		+ Scale<Self::BlockNumber, Output = Self::Moment> + Copy;
 
 	/// Something which can be notified when the timestamp is set. Set this to `()` if not needed.