Add challenge result endpoint

[jmgasper]

We need a way to grab challenge results, to aid in ratings calculations. Something that holds:

Input

Challenge ID

Output

• List of submitters
  • Submission ID
  • Member handle / ID
  • Placement of the submission (if applicable / passed review)
  • Score
    • Final score
    • Each individual review score
      • Reviewer handle / ID
      • Review score from that reviewer

SRMs

One thing we have to handle is SRMs, which currently exist outside the "challenge" flow. If we can somehow import SRMs into the challenge object (with minimal data) and then define reviews based on system scores, that may work, but I'm open to suggestions. Have a look here to get an idea of what SRM data we have:

https://archive.topcoder.com/ProblemArchive