* Fix bug in inCurrentEpoch and improve accumulator related tests
- Fix negative wraparound / underflow in inCurrentEpoch
- Add tests in accumulator tests to verify the above
- Add header offer tests with accumulator that does and doesn't
contain historical epochs
- Additional clean-up of history tests
- enable canonicalVerify in the tests
* Add a basic ContentDB for Portal networks
* Use ContentDB in StateNetwork
* Avoid probably some form of sandwich problem by re-exporting kvstore_sqlite3 from content_db