Adds stats to the sprint demo rake task

[nathanstitt]

No description provided.

[nathanstitt]

The user teacher accessed /api/plans/1 and got:

{
  "id": 4,
  "type": "reading",
  "opens_at": "2015-03-24T21:20:11.074Z",
  "due_at": "2015-03-31T21:20:11.074Z",
  "settings": {
    "page_ids": [
      1,
      2,
      3
    ]
  },
  "stats": {
    "course": {
      "total_count": 31,
      "complete_count": 16,
      "partially_complete_count": 16,
      "current_pages": [
        {
          "page": {
            "id": 1,
            "number": 1,
            "title": "Introduction"
          },
          "student_count": 0,
          "correct_count": 0,
          "incorrect_count": 0
        },
        {
          "page": {
            "id": 2,
            "number": 2,
            "title": "Force"
          },
          "student_count": 31,
          "correct_count": 14,
          "incorrect_count": 2
        },
        {
          "page": {
            "id": 3,
            "number": 3,
            "title": "Newton's First Law of Motion: Inertia"
          },
          "student_count": 31,
          "correct_count": 22,
          "incorrect_count": 10
        }
      ],
      "spaced_pages": [
        {
          "page": {
            "id": 0,
            "number": 0,
            "title": ""
          },
          "student_count": 31,
          "correct_count": 51,
          "incorrect_count": 13
        }
      ]
    },
    "periods": [

    ]
  }
}

[jpslav]

to target a specific TP without worrying about order, you can just return the task plan of interest from the sprint routine.