* Upgrade geth from 1.8.15 to 1.8.18
* Update vat_tune to use shared repository methods
* Query blockchain by block hash instead of block number range
* Remove hash validation from repositories
* Fix vow flog integration test
* Update README Travis build sticker
* Update constants formatting per go fmt
* Update EthPublicKeyParser.ParsePublicKey to use discv5.PubkeyID method
* Address PR comments
* Add constants for TTL and tic for fakeHeader
* Add tic to tend transformer
* Update tests for tend
* Fix string conversion bug in fakes
* Fix tend integration tests after staging rebase
* Add tic to dent transformer
* Update dent tests
* Change integration tests to use hardcoded block timestamp
- Delete header on conflict to prompt data refresh (cascade deletes all
data associated with that block)
- Derive header hash from rpc payload rather than computing it from data
(prevents hash mismatch between blockchain and cache)
