Improve "Reset Everything"

[psztorc]

1. The "Reset Everything" button currently deletes all sidechains and allows the user to re-download them.

2. It should first move the wallets to a new folder "drivechain_launcher_wallets" ...to back them up

3. Ideally, it would also restore those wallets. This would trigger upon a successful sidechain download, Launcher checks "drivechain_launcher_wallets" to see if there is a wallet for the newly-downloaded chain. If so it copies it over.

4. Separately, we should have "Reset Chain" -- an option for each chain. Instead of nuking all chains, it should just nuke the one single chain.