TransactionCoordinator updated for non blocking

TransactionCoordinator is utilized when working with transactions. Unfortunately due to transaction API being inherently blocking, we need to make some exceptions to how this is handled.

1. TransactionCoordinator should only be invokable by a blocking method, the inverse of the PersistenceManagerImpl
2. We should invoke all the non blocking code of TransactionCoordinator in a non blocking thread and then block on its completion in the blocking thread.