Code review comment for ~pappacena/launchpad:change-override-log

cjwatson, this is still a WIP (I'm still missing tests, for example), but I would like to get a "pre-review", just to make sure we are aligned on what should be done here.

Basically, I checked lp:ubuntu-archive-tools repo and it seems that the `change-override` scripts call the changeOverride on the API, with an authenticated user.

So, on LP side, I'm getting the logged in user and setting it on the "creator" field both for Source and Binary PackagePublishingHistory. Then, showing it on the details of the +publishinghistory page.