enhancement: store sender wallet address

[ErinHales]

It seems if I use sender as the query param, I have fewer transactions in my history than if I use recipient. One possibility is that we could be storing the ETH Helper as the sender instead of the user's address. You should be able to query the Send event on the ETH Helper to get the correct sender.

[kekonen]

This has to wait till v2, as it is too much of a hustle to implement right now