Add custom narrative to the FHIR Encounter Resource

The FHIR Encounter Resource may include a human-readable narrative that contains a summary of the resource, and may be used to represent the content of the resource to a human.
We agreed to define an OpenMRS specific narrative instead of the default narrative currently provided by the HAPI FHIR API

Resources

FHIR HL7 Documentation: http://www.hl7.org/implement/standards/fhir/narrative.html