Cannot be cast to javassist.util.proxy.Proxy error

@ibacher Is there any other method other than importing the ca.uhn.fhir.context.FhirContext because I tried it but it throws error due to clash between ca.uhn.fhir & org.hl7.fhir

(Need FHIR2 encounter create and update calls - #15 by ibacher)

I used SimpleContextWorker in the place of FhirContext due to these reasons.