Closes: #4530
This PR contains logic for both submitting an evidence by the light client (lite2 package) and receiving it on the Tendermint side (/broadcast_evidence RPC and/or EvidenceReactor#Receive). Upon receiving the ConflictingHeadersEvidence (introduced by this PR), the Tendermint validates it, then breaks it down into smaller pieces (DuplicateVoteEvidence, LunaticValidatorEvidence, PhantomValidatorEvidence, PotentialAmnesiaEvidence). Afterwards, each piece of evidence is verified against the state of the full node and added to the pool, from which it's reaped upon block creation.
* rpc/client: do not pass height param if height ptr is nil
* rpc/core: validate incoming evidence!
* only accept ConflictingHeadersEvidence if one
of the headers is committed from this full node's perspective
This simplifies the code. Plus, if there are multiple forks, we'll
likely to receive multiple ConflictingHeadersEvidence anyway.
* swap CommitSig with Vote in LunaticValidatorEvidence
Vote is needed to validate signature
* no need to embed client
http is a provider and should not be used as a client
