Change DNStateManager to use Persistable and drop generics #376
Description
The generics option would have allowed us to permit enhancement to other contracts (e.g JDO reference bytecode), but the absence of people on this project mean that will never happen, so let's simplify it all. Likely will impact on API calls down into store plugins, so has a major impact. Wait for 6.0
Other classes involved
ExecutionContext
CachedPC
StateManagerFactory
StateManagerImpl