Improving serialization to use first byte as an identifier for partial puts.

- Adding fixes based on comments to the last pull request.
https://github.com/clementfung/voldemort/pull/2

- Adding a serialization step in which a '0' is appended to the front of the ByteArray. Also, removed the ugly cast of the key into String.
- Adding a flag to disable Venice if ConsistentRouting is not used. Based on the way the Kafka Producer works, using any other routing strategy would be a hack.
Can we define these as constants in only one place? Not sure what the best place is, but DRY is good.