State of user as on point of tracking

As explained on https://keybase.io/docs/tracking, tracking is taking a snapshot of a user's identity at a given time and signing it with my own key. Now I'd like to be able to view that snapshot via the web UI and even better, see the difference between the captured state and the current state.

Start with the tracking overview at https://keybase.io/docs/tracking to understand the captured identity state and its signing context. Done means the web UI can display a user's tracked snapshot and show the differences between that snapshot and the current state.

Written by the indexing model from the issue text.