* beefy-mmr: reuse sp_runtime::traits::Keccak256
* beefy-mmr: use sp_runtime::traits:Hash for generating merkle proofs
* beefy-mmr: use sp_runtime::traits:Hash for validating merkle proofs
* beefy-mmr: remove primitives::Hasher and primitives::Hash
* fixes
* beefy-mmr: reduce the number of generic parameters for merkle_root()
* fix
* compute upper Vec capacity more accurately