Sort code violations by dateEntered instead of caseId

Before (when we didn't have valid dates), we were sorting all of the code violations on a field called caseId. This was a pretty arbitrary thing to do. Now that we have dates, let's make sure that code violations returned from the API are sorted in reverse chronological order. This pull request changes the functionality of the API to do just that. Now `homes/:homeId/violations` will return a JSON object containing each violation sorted in reverse chronological order by the `dateEntered` field