Replace all Rlp usages with UntrustedRlp except for ethcore views (#8233)

* Replace Rlp with UntrustedRlp and unsafely unwrap

All Rlp methods return Result<_,DecoderError> now, so for this first
pass each will be marked with `expect("TODO")`. In the next pass we can
categorise figure out how to handle each case.

* Handle DecoderError for tendermint message

* Unwrap rlp results in TestBlockcChainClient

Rlp should be valid since created manually in tests

* Replace `use rlp::*` with explicit imports

* Remove rlp decode unwraps from light cli request

* Structured rlp encoding for curr best and latest in header chain

* Propogate decoder errors from send_packet

* Fix body uncles rlp index

* Use BodyView in sync and `expect` rlp errors

* Revert bbf28f removing original Rlp for this phase

This can be done again in the next phase, in order that we can leave the ethcore views unchanged

* Restore legacy Rlp and UntrustedRlp

Use legacy Rlp for ethcore views. Will redo replacing Rlp with UntrustedRlp in  a subsequent PR

* Fix tests

* Replace boilerplate Encodable/Decodable with derive

* Use BlockView instead of Rlp, remove unwrap

* Remove rlp test_cli unwraps by using BlockView instead of Rlp directly

* Remove unneccesary change to use borrowed hash

* Construct sync block using new_from_header_and_body