* add a new RPC `eth_submitWorkDetail`similar `eth_submitWork`.
It has more details (block hash, error message, and more in future)
in its response and not only the `true` or `false`.
* move RPC submitWorkDetail from namespace eth_ to parity_
* remove SubmitDetailResult type; submitWorkDetail return a error when failed
* change error message of RPC error `cannot_submit_work`.
* remove double imported H256.
* put submit_work_detail into a helper to avoid the duplicate codes.
