Support for upgrading from 1.9 and 2.0

- added support for reading 1.9 and 2.0 log files
- fix: PhysicalLogNeoCommandReaderV0 should parse 1.9 commands
We do not currently have version for 2.2, which needs it as the log entry format has changed. -2 will do just fine as a value since we still support Neo4j versions  which do not have versioned log entries (and they must be identified by the positive first byte)