* types: change `Commit` to consist of just signatures
These are final changes towards removing votes from commit and leaving
only signatures (see ADR-25)
Fixes#1648
* bring back TestCommitToVoteSetWithVotesForAnotherBlockOrNilBlock
+ add absent flag to Vote to indicate that it's for another block
* encode nil votes as CommitSig with BlockIDFlagAbsent
+ make Commit#Precommits array of non-pointers
because precommit will never be nil
* add NewCommitSigAbsent and Absent() funcs
* uncomment validation in CommitSig#ValidateBasic
* add comments to ValidatorSet funcs
* add a changelog entry
* break instead of continue
continue does not make sense in these cases
* types: rename Commit#Precommits to Signatures
* swagger: fix /commit response
* swagger: change block_id_flag type
* fix merge conflicts
* types.NewCommit
* use types.NewCommit everywhere
* fix log in unsafe_reset
* memoize height and round in constructor
* notes about deprecating toVote
* bring back memoizeHeightRound
Addressing some feedback from @ebuchman in regards to
consolidating some common test headers into a variable.
I've added that for simple cases, trying to meet in the middle
instead of creating helpers that obscure readibility and easy
comparison of test cases.
Anton Kaliaev
Ethan Buchman
Zach Ramsay
Jae Kwon
Liamsi
Emmanuel T Odeke