Alter event on client updates to emit full header

[cwgoes]

This will make misbehaviour handling (which requires tracking these headers) easier.

This should be done on a non-breaking point release off the Stargate branch, so that Stargate full nodes can run it.

[cwgoes]

cc @ancazamfir

[ancazamfir]

This looks good.
One other question is about client create and the expected validation for the misbehavior detector.
Discussed this with @milosevic offline and we think we do not need the header in the create event and message as we cannot submit misbehavior in this case. The detector would:

• monitor CreateClient event
• fetch header at consensus height from full node
• ensure the consensus state derived from the header is identical to the one on-chain
• if not then "blacklist" that client

Not clear what "blacklist" means and what can be done. Locally we can make sure the relayer will not use that client.

The other topic we discussed is the misbehavior detector after a restart. If it finds a conflicting header (different trusted validator set) at latest consensus height, it needs to go backwards through the client updates to find where the misbehavior happened.
Trying to get away with an (almost-)stateless relayer here.

Any thoughts on this @cwgoes? @milosevic please feel free to correct/ add.

[maybe not the best github issue to use for this discussion, though I don't mind].