LoadState
Method for loading PersistedState from SharedPreferences. Attempts to retrieve the data via a key. If found, deserializes the data and returns an persistenceSerializer of PersistedState. Otherwise, will initialize a new persistenceSerializer with an auto-generated respondent ID (should only happen once).
Return
the PersistedState that is stored in SharedPreferences (or a newly instantiated one)
Parameters
context
Throws
potential for serialization exceptions