Enable easy rolling back to your own local statesync snapshot

[ValarDragon]

Summary

Currently there is no convenient method to roll back to a state snapshot that you have on your own machine. However all of the data is there (as your node will be serving it to other nodes) We should make it possible to revert your node back to a local snapshot.

As a validator, this would save me from so many issues when I accidentally do something that corrupts part of the db, and I am forced to revert my state. At the moment I have to download from a snapshot, as state sync was broken for several SDK, Tendermint version pairings, or re-state sync on pairings that work.

At upgrade time, there are a class of issues for which this is immensely helpful.

As a developer, it is very convenient to be able to quickly roll back to test something about a prior chain version, or test performance improvements against the live chain.

Proposal

Build a command that makes your own node roll back state to a prior version it has snapshotted for state sync.

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[tac0turtle]

This is a super needed feature also allowing someone to stop their node, snapshot, delete all other data, then restore from that snapshot would be amazing. To do both of these I believe we need the commit store exposed on the app.

[tac0turtle]

completed and backported to 0.46 & 0.47