* Remove db from tendemrint in favor of tendermint/tm-cmn

- remove db from `libs`
- update dependancy, there have been no breaking changes in the updated deps
	- https://github.com/grpc/grpc-go/releases
	- https://github.com/golang/protobuf/releases

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* changelog add

* gofmt

* more gofmt

* Expose priv validators for use in testing

* Generalize block header validation test past height 1

* Remove ineffectual assignment

* Remove redundant SaveState call

* Reorder comment for clarity

* Use the block executor ApplyBlock function instead of implementing a stripped-down version of it

* Remove commented-out code

* Remove unnecessary test

The required tests already appear to be implemented (implicitly) through
the TestValidateBlockHeader test.

* Allow for catching of specific error types during TestValidateBlockCommit

* Make return error testable

* Clean up and add TestValidateBlockCommit code

* Fix formatting

* Extract function to create a new mock test app

* Update comment for clarity

* Fix comment

* Add skeleton code for evidence-related test

* Allow for addressing priv val by address

* Generalize test beyond a single validator

* Generalize TestValidateBlockEvidence past first height

* Reorder code to clearly separate tests and utility code

* Use a common constant for stop height for testing in state/validation_test.go

* Refactor errors to resemble existing conventions

* Fix formatting

* Extract common helper functions

Having the tests littered with helper functions makes them less easily
readable imho, so I've pulled them out into a separate file. This also
makes it easier to see what helper functions are available during
testing, so we minimize the chance of duplication when writing new
tests.

* Remove unused parameter

* Remove unused parameters

* Add field keys

* Remove unused height constant

* Fix typo

* Fix incorrect return error

* Add field keys

* Use separate package for tests

This refactors all of the state package's tests into a state_test
package, so as to keep any usage of the state package's internal methods
explicit.

Any internal methods/constants used by tests are now explicitly exported
in state/export_test.go

* Refactor: extract helper function to make, validate, execute and commit a block

* Rename state function to makeState

* Remove redundant constant for number of validators

* Refactor mock evidence registration into TestMain

* Remove extraneous nVals variable

* Replace function-level TODOs with file-level TODO and explanation

* Remove extraneous comment

* Fix linting issues brought up by GolangCI (pulled in from latest merge from develop)

What happened:

New code was supposed to fall back to last height changed when/if it
failed to find validators at checkpoint height (to make release
non-breaking).

But because we did not check if validator set is empty, the fall back
logic was never executed => resulting in LoadValidators returning an
empty validator set for cases where `lastStoredHeight` is checkpoint
height (i.e. almost all heights if the application does not change
validator set often).

How it was found:

one of our users - @sunboshan reported a bug here
https://github.com/tendermint/tendermint/pull/3537#issuecomment-482711833

* use last height changed in validator set is empty
* add a changelog entry

* rpc: store validator info periodly

* increase ValidatorSetStoreInterval

also

- unexpose it
- add a comment
- refactor code
- add a benchmark, which shows that 100000 results in ~ 100ms to get 100
validators

* make the change non-breaking

* expand comment

* rename valSetStoreInterval to valSetCheckpointInterval

* change the panic msg

* add a test and changelog entry

* update changelog entry

* update changelog entry

* add a link to PR

* fix test

* Update CHANGELOG_PENDING.md

Co-Authored-By: melekes <anton.kalyaev@gmail.com>

* update comment

* use MaxInt64 func