Ref #3 - Refactor to speed things up / clarify

- Renamed the collection variables in use to more closely match their class
  names
- Now only parsing the HQMF documents necessary for exporting a single CAT1 set
  of XML - saves a couple of minutes
- Now only generating QualityReport instances for the measure in question -
  saves even more time
- Total time to run an export for a single CAT1 test down from 6-7 minutes to
  <30 seconds