Improve the inheritance architecture of the contracts by using overriding public variables

[clemlak]

While studying Uniswap v3, I've recently discovered that public variables can override a constant function defined in an interface. For example, the function token0() defined here in the IUniswapV3PoolImmutables.sol interface is then overridden by the public variable token0 defined here in the child contract UniswapV3Pool.

This means that our current inheritance architecture could be improved by changing our current flow from:

Storage (abstract contract) -> Interface (abstract contract) -> Logic (contract)

to:

Interface (interface) -> Storage (abstract contract) -> Logic (contract)

Additionally, all the struct and enum types will have to be defined directly into the interface.

I think this change would make the architecture simpler and more logic.

[PaulRBerg]

Done via #36.