Convert Serializer into DiskPersistence

[abhishekraok]

Serializer was created before when persistence and graph was not separated well. Serializer was used to save graph to disk and Azure.

Currently serializer is shoehorned into the PersistenceInterface.
Convert existing serializer into DiskPersistence, CloudPersistence similar to MemoryPersistence. DiskPersistence can take the base directory in disk where the graph will be stored. CloudPersistence can take the account details (e.g. Azure path, key) and save in cloud.