* Prevote nil if not timely
* William's suggestion to get the proposal from the proposer instead of
generating it.
* Don't check rhs for genesis block
* Update IsTimely to match the specification
* Fix proposal tests
* Add more timely tests and check votes
* Mark proposal invalid in SetProposal, fix in the future test
* save proposal time on roundstate
* received -> receive
* always reset proposal time
* Add IsTimely test for genesis proposal
* Check timely before ValidateBlock
* Review comments from Daniel
Co-authored-by: William Banfield <wbanfield@gmail.com>