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/example/src/lib.rs

@@ -651,7 +651,8 @@ mod tests {
 	// The testing primitives are very useful for avoiding having to work with signatures
 	// or public keys. `u64` is used as the `AccountId` and no `Signature`s are required.
 	use sp_runtime::{
-		Perbill, testing::Header,
+		Perbill,
+		testing::Header,
 		traits::{BlakeTwo256, OnInitialize, OnFinalize, IdentityLookup},
 	};