We don't need to clear keccak context after hashing ethereum data since
it is already public - similar to
https://github.com/status-im/nimbus-eth2/pull/222.
Because we overwrite the result fully, we also don't need to zero first.
`eth_types` is being imported from many projects and ends up causing
long build times due to its extensive import lists - this PR starts
cleaning some of that up by moving the chain DB and RLP to their own
modules.
this PR also moves `keccakHash` to its own module and uses it in many
places.
Jacek Sieka
tersec