Consider clearing other address info when user changes city/state

[toolness]

As I'm working on #1302 I'm realizing that it might be possible for the user to weirdly navigate around the flow in such a way that they set a city/state, set a national address, then go back and change their city/state, then skip past setting the national address, and we may be left with a nonsensical address even though we did validation in all the steps.