[BACK-2540] Reports api

[jh-bate]

Single user report API request (assuming we include multiple users reports later) This is from the working example that @krystophv and I have worked on in the export service to be accessed by blip also

Implementation tidepool-org/export#43

also included:

• update for common glucose units reference
• update response errors to have relevant code and messages as examples
• update to reference common MRN definition

[toddkazakov]

Making changes to clinic service models is undesirable, because the clinic and server stubs are generated from this spec. I have previously found the deep references are not well supported by the code generator and cause issues.

[jh-bate]

all done @toddkazakov - I have removed that update