* separate modules for consensus snapshot chunks
* bulk of authority warp logic
* finish authority warp implementation
* squash warnings and enable authority snapshot mode
* test harness for PoA
* fiddle with harness
* epoch generation proof fixes
* update constructor code
* store epoch transition proof after block commit
* basic snap and restore test
* use keyvaluedb in state restoration
* decompress chunks
* fix encoding issues
* fixed-to-contract-to-contract test
* implement ancient block import
* restore genesis transition in PoW snapshot
* add format version method to snapshot components
* supported version numbers in snapshot_components
* allow returning of ancient epoch transitions
* genesis hash mismatch check
* remove commented code
* clarify "cancelled periodic snapshot" message
* more rigorous checks for snapshot validity
* verify ancient blocks on import
* limit number of fed blocks
* make it possible to feed snapshot service canonical hashes
* fix failing test build
* swap ethash DAG only when more recent
