* 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
