Initial validator sets pallet (#187)

* Initial work on a Validator Sets pallet

* Update Validator Set docs per current discussions

* Update validator-sets primitives and storage handling

* Add validator set pallets to deny.toml

* Remove Curve from primitives

Since we aren't reusing keys across coins, there's no reason for it to be
on-chain (as previously planned).

* Update documentation on Validator Sets

* Use Twox64Concat instead of Identity

Ensures an even distribution of keys. While xxhash is breakable, these keys
aren't manipulatable by users.

* Add math ops on Amount and define a coin as 1e8

* Add validator-sets to the runtime and remove contracts

Also removes the randomness pallet which was only required by the contracts
runtime.

Does not remove the contracts folder yet so they can still be referred to while
validator-sets is under development. Does remove them from Cargo.toml.

* Add vote function to validator-sets

* Remove contracts folder

* Create an event for the Validator Sets pallet

* Remove old contracts crates from deny.toml

* Remove line from staking branch

* Remove staking from runtime

* Correct VS Config in runtime

* cargo update

* Resolve a few PR comments on terminology

* Create a serai-primitives crate

Move types such as Amount/Coin out of validator-sets. Will be expanded in the
future.

* Fixes for last commit

* Don't reserve set 0

* Further fixes

* Add files meant for last commit

* Remove Staking transfer

substrate/validator-sets/primitives/src/lib.rs

@@ -0,0 +1,21 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use scale::{Encode, Decode, MaxEncodedLen};
+use scale_info::TypeInfo;
+#[cfg(feature = "std")]
+use serde::{Serialize, Deserialize};
+
+/// The type used to identify a specific session of validators.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct Session(pub u32);
+
+/// The type used to identify a validator set.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct ValidatorSetIndex(pub u16);
+
+/// The type used to identify a specific validator set during a specific session.
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, TypeInfo, MaxEncodedLen)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct ValidatorSetInstance(pub Session, pub ValidatorSetIndex);