Coins pallet (#399)

* initial implementation

* add function to get a balance of an account

* add support for multiple coins

* rename pallet to "coins-pallet"

* replace balances, assets and tokens pallet with coins pallet in runtime

* add total supply info

* update client side for new Coins pallet

* handle fees

* bug fixes

* Update FeeAccount test

* Fmt

* fix pr comments

* remove extraneous Imbalance type

* Minor tweaks

---------

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

substrate/coins/primitives/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "serai-coins-primitives"
+version = "0.1.0"
+description = "Serai coins primitives"
+license = "MIT"
+authors = ["Luke Parker <lukeparker5132@gmail.com>"]
+edition = "2021"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[dependencies]
+zeroize = { version = "^1.5", features = ["derive"], optional = true }
+
+serde = { version = "1", default-features = false, features = ["derive", "alloc"] }
+
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }
+scale-info = { version = "2", default-features = false, features = ["derive"] }
+
+serai-primitives = { path = "../../primitives", default-features = false }
+
+[dev-dependencies]
+sp-runtime = { git = "https://github.com/serai-dex/substrate", default-features = false }
+
+[features]
+std = ["zeroize", "serde/std", "scale/std", "scale-info/std", "sp-runtime/std", "serai-primitives/std"]
+default = ["std"]