Save gas by using a ParameterizerInterface in Registry

Presently, `Registry.sol` imports `Parameterizer.sol` in its entirety, but only calls the function `get(string _name)`.

You can save gas and storage space by using a `ParameterizerInterface.sol` in `Registry`
```solidity
interface ParameterizerInterface {
        function get(string _name) public view returns (uint value);
}
```