Track tags in game history

[dfabulich]

Tagging could/should be tracked in game history, so anyone can see who tagged a game and when.

[dfabulich]

If/when we roll this out, I think we might want to write some code to retroactively add in game-history events for added tags. We could either do them fine grained, adding individual fake history events for every added tag, or we could just do one big history event for every game to say that the "system" added these tags to history.

[dfabulich]

I mentioned this on #873, but I wanted to mention it here, too: I think if we do this, it would be fine for anyone to remove tags.

[jtn20]

If tags do become part of game data and history (per this and #915), I think the game history viewer will need enhancement, as tag changes will make game edit history very noisy.
I'd like to be able to continue to see just the changes that affect non-tag bits of game data, as today.
(But, of course, we also need to be able to see a history view that includes tag changes, otherwise we don't have the implicit monitoring abuse from having a public audit trail.)