Store history of level hash for levels

[jvyden]

Useful for contests so judges can properly verify if levels were modified after the submission period has ended.

[Beyley]

There is an implementation of this here (but only for a game endpoint [non-standard endpoint? it doesn't exist in any game I checked]).
I think taking some inspiration from that implementation and expanding this issue to generalized level info history is a good idea, since storing icon/name/description history would be very useful for moderation, so I think we should do something similar to how ennuo implemented it, where name, description, icon, root hash are all stored in the history as well.