Create working medication structure

-Fixed several issues caught by the NIST validation tool
-Fixed typos in templateId
-Added nested elements where needed
-Added a structuredBody element. Note that this is required by the
HL7 spec but not mentioned in the HITSP spec. Currently trying to
resolve whether to accommodate both. This is highly dependent on the
parser that consumes these documents.
-This medication structure can be imported by Epic EMR