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/im-online/src/lib.rs

@@ -79,7 +79,7 @@ use pallet_session::historical::IdentificationTuple;
 use sp_runtime::{
 	offchain::storage::StorageValueRef,
 	RuntimeDebug,
-	traits::{Convert, Member, Saturating, SimpleArithmetic}, Perbill,
+	traits::{Convert, Member, Saturating, AtLeast32Bit}, Perbill, PerThing,
 	transaction_validity::{
 		TransactionValidity, ValidTransaction, InvalidTransaction,
 		TransactionPriority,
@@ -151,7 +151,7 @@ struct HeartbeatStatus<BlockNumber> {
 	pub sent_at: BlockNumber,
 }
 
-impl<BlockNumber: PartialEq + SimpleArithmetic + Copy> HeartbeatStatus<BlockNumber> {
+impl<BlockNumber: PartialEq + AtLeast32Bit + Copy> HeartbeatStatus<BlockNumber> {
 	/// Returns true if heartbeat has been recently sent.
 	///
 	/// Parameters: