Staking pallet (#373)

* initial staking pallet

* add staking pallet to runtime

* support session rotation for serai

* optimizations & cleaning

* fix deny

* add serai network to initial networks

* a few tweaks & comments

* fix some pr comments

* Rewrite validator-sets with logarithmic algorithms

Uses the fact the underlying DB is sorted to achieve sorting of potential
validators by stake.

Removes release of deallocated stake for now.

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

substrate/primitives/src/networks.rs

@@ -1,6 +1,3 @@
-#[cfg(feature = "std")]
-use std::collections::HashMap;
-
 #[cfg(feature = "std")]
 use zeroize::Zeroize;
 
@@ -120,12 +117,3 @@ impl Network {
     &self.coins
   }
 }
-
-#[cfg(feature = "std")]
-lazy_static::lazy_static! {
-  pub static ref NETWORKS: HashMap<NetworkId, Network> = HashMap::from([
-    (NetworkId::Bitcoin, Network::new(vec![Coin::Bitcoin]).unwrap()),
-    (NetworkId::Ethereum, Network::new(vec![Coin::Ether, Coin::Dai]).unwrap()),
-    (NetworkId::Monero, Network::new(vec![Coin::Monero]).unwrap()),
-  ]);
-}