adding upgrade code for upgrading from 0.9.7 to 0.9.8.

Will keep a set of codecs for serializing/deserializing current
objects, and a separate set for converting between versions.
Switched to use guice injection to create the codec everywhere.
aside from getting the gson, JsonSerde is only used to transform strings into bytes and vice versa, so we could just get rid of it and bind Gson in the codec module.  will do that.