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/society/src/mock.rs

@@ -23,7 +23,9 @@ use sp_core::H256;
 // 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 requried.
 use sp_runtime::{
-	Perbill, traits::{BlakeTwo256, IdentityLookup, OnInitialize, OnFinalize}, testing::Header,
+	Perbill,
+	testing::Header,
+	traits::{BlakeTwo256, IdentityLookup, OnInitialize, OnFinalize},
 };
 use frame_system::EnsureSignedBy;