* pallet-mmr: cosmetic improvements
* pallet-mmr: fix offchain storage for initial sync
* address review comments
* pallet-mmr: change offchain fork-resistant key to `(prefix, pos, parent_hash)`
Do this so that both canon and fork-resitant keys have the same
`(prefix, pos).encode()` prefix. Might be useful in the future if we'd
be able to to "get" offchain db entries using key prefixes as well.
Signed-off-by: acatangiu <adrian@parity.io>
Signed-off-by: acatangiu <adrian@parity.io>