Mujir | #457 | No validation for encounters import. More refactorings.
1. Encounters import would not run validation stage. So no validations needed.
2. BahmniEncounterTransaction save now handles string encountertype
3. Introduced a RetrospectiveEncounterTransactionService that can be used to save any past encounters. It will not import duplicate diagnoses/observations. Its in admin module, can be moved into a more common module when needed.