Error on updating HL7Message object with content

[id2359]

Instantiation of HL7Message object fails as content update causes Assertion error fails.

Split the message object creation into two: initial and annotation with actual content.

I'm pretty this is a side effect of going from python-hl7 0.4.2 to 0.4.5

So we should roll back to 0.4.2

This ticket is just to try to save the message model.