Allow for earliest to latest chifra init --

[tjayrush]

At one point, we were downloading gnosis chain from Unchained index, and the Pinata started throwing 403 errors. It had downloaded between blocks 6,000,000 and 39,000,000 which means there was a gap. There was not way to backfill. But there could have been with either a --backfill option on scraper or --backwards option on chifra init.

(In either case, the above should reference khedra not chifra init)