Track the full history of all changes to polling places and expose the history of it to admins

[keithamoss]

This would appear as a 'History' tab/button/thing on each polling place.

And separately by related, also expose the last 10 or so stalls that have been changed somewhere - this would benefit H.

How would this work with the polling place loading en masse? Can we do a staged approach where we keep the current approach to 'versioning' polling places for en masse loads and just add in change tracking for individual edits?

We've never used the 'rollback to snapshotted en masse loaded polling places', so why have all of the code to keep it going when we could just turn on model history and be done with it?