* All Contract Upgrade functionality performed within a corresponding flow.
Removed RPC API calls for contract upgrade authorisation / de-authorisation.
Added persistence using AppendOnlyPersistentMap.
* Changed to using a PersistentMap to ensure entries can be removed (was causing failing de-authorisation tests).
Fixed all warnings.
* Added mandatory @Suspendable annotations to flows.
* Do not instantiate object unless overridden.
* Updated changelog and CordaDocs.
* Persistence simplification: only store upgrade contract class name (not serialized object)
* Remove nullability from contract_class_name DB column.
Fixup tests after rebase
Add unit tests of Persistent Identity. Fix bugs in PersistentMap.
Wrap identity and network map RPC calls in database transaction
Address PR comments
