Add an oldAddress param to AddressSet event

[laizy]

Is your feature request related to a problem? Please describe.

Currently, the AddressSet event is defined as:

 event AddressSet(
        string _name,
        address _newAddress
    );

But the data-transport-layer service wants the old address, so have to do some searching to find the previous address set event,
which makes the code more complex and is not efficient enough.

Describe the solution you'd like
Add oldAddress param to the events.

 event AddressSet(
        string _name,
        address _newAddress,
       address _oldAddress
    );

[smartcontracts]

100% agree with this. I had a PR that made this exact change in our old contracts repo: https://github.com/ethereum-optimism/contracts/pull/224/files. We should make this change ASAP.

[smartcontracts]

Closed by #820, will be released in 0.4.0