Make Balances Configurable

There is nothing new to learn in this step, just repeating the same process we did for our System Pallet for the Balances pallet.

In this case, our Config trait will only have two associated types: AccountId and Balance.

For this step, try to avoid looking at the solution, and instead refer to the changes you made to get the System Pallet configurable.

1. Define the Config trait which will have your associated types.
2. Make sure these types have their trait constraints defined in Config.
3. Update your struct Pallet to use T: Config and reference your types using the T:: syntax.
4. Update all of your functions to use the T:: syntax.
5. Update your test, creating a struct TestConfig, and implementing Config for it, and using it to instantiate your Pallet struct.
6. Go to your main.rs file, and implement balances::Config for the Runtime struct.
7. Update your Runtime definition to instantiate balances::Pallet with Self.

If you have made it this far, I think it is fair to say you have made it over the hardest part of this tutorial, and the hardest part of using Rust in Substrate.

It is important to take a step back and remember that while these abstractions make your code a bit more complicated to fully understand, it also makes your code extremely flexible, at zero cost to performance and safety thanks to the Rust compiler.