add in some new mock responses for our staff grading API

lms/static/coffee/src/staff_grading/staff_grading.coffee

@@ -18,10 +18,15 @@ class StaffGradingBackend
 
   mock: (cmd, data) ->
     # Return a mock response to cmd and data
+    # should take a problem id as an argument
     if cmd == 'get_next'
       @mock_cnt++
       response =
         success: true
+        problem_name: 'Problem 1'
+        num_left: 3
+        num_total: 5
+        prompt: 'This is a fake prompt'
         submission: 'submission! ' + @mock_cnt
         rubric: 'A rubric! ' + @mock_cnt
         submission_id: @mock_cnt
@@ -32,6 +37,16 @@ class StaffGradingBackend
       console.log("eval: #{data.score} pts,  Feedback: #{data.feedback}")
       response =
         @mock('get_next', {})
+    # get_probblem_list
+    # sends in a course_id and a grader_id
+    # should get back a list of problem_ids, problem_names, num_left, num_total
+    else if cmd == 'get_problem_list'
+        response = 
+            success: true
+            problem_list: [
+                {problem_id: 1, problem_name: "Problem 1", num_left: 3, num_total: 5}
+                {problem_id: 2, problem_name: "Problem 2", num_left: 1, num_total: 5}
+            ]
     else
       response =
         success: false