Adding rake task to convert measure ids

- New rake task in bonnie.rake to convert a record/patient's measure_ids
  list from the NQF ids to the HQMF ids.
- Also added a tiny fix to Janoo's expected value code in the measure
  model that ensures there is a population before trying to get info
  from it. (line 29, added ? after pops) This was required for me to be
  able to see the measure list on the dashboard.
Patients are now associated with multiple measures

- Code in application.html.erb now adds each patient to every measure in
  their list of measure ids. This can be seen on the dashboard by
  looking at the small part of the fraction under test patients.
- Added another null check to expected value code to check for the
  population's existence before calculating.