Implement the PractitionerRole Resource

The PractitionerRole resource is specified here. Please note that this resource models the clinical role of the practitioner and not the security role. We should at least be able to provide:

• practitioner - this is just a reference to the practitioner resource
• code - see this value set; `doctor` | `nurse` | `pharmacist`
• specialty - SNOMED codes are preferred, but may not be that straight-forward to implement. At the very least, we should be able to sent the corresponding code from OpenMRS.
• telecom - using the translator for this that already exists
• active - whether or not the provider has been voided.