set student progression pagination container

test plan:
 - have a course with more than 50 students and only one module
 - go to /courses/X/modules/progressions in a full-screen
   browser window (the key here is that the page needs to fit
   in the window vertically so there is no scrollbar attached
   to the window)
 - scroll down through the list of students on the right side
 - the second page of students should load
 - also, test viewing this page as a student (you should still
   see your own progression on the left)

I suggest testing in Firefox because Chrome sends a Window
scroll event even when there is nowhere to scroll

fixes CNVS-14255

Change-Id: Ib12b44e9d047b35193913be5e91e1f9dee74fa43
Reviewed-on: https://gerrit.instructure.com/38749
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>

app/coffeescripts/bundles/context_module_progressions.coffee

@@ -17,15 +17,20 @@ require [
         per_page: 50
         enrollment_type: 'student'
 
-    students.fetch()
-
   indexView = new PaginatedCollectionView
     collection: students
     itemView: ProgressionStudentView
     template: progressionsIndexTemplate
     modules_url: ENV.MODULES_URL
+    autoFetch: true
+
+  unless ENV.RESTRICTED_LIST
+    # attach the view's scroll container once it's populated
+    students.fetch success: ->
+      indexView.resetScrollContainer(indexView.$el.find('#progression_students .collectionViewItems'))
 
   indexView.render()
   if ENV.RESTRICTED_LIST && ENV.VISIBLE_STUDENTS.length == 1
     indexView.$el.find('#progression_students').hide()
   indexView.$el.appendTo($('#content'))
+

app/coffeescripts/views/PaginatedCollectionView.coffee

@@ -55,6 +55,16 @@ define [
       super
       @initScrollContainer()
 
+    ##
+    # Set the scroll container after the view has been created.
+    # Useful if the view is created before the container is rendered.
+
+    resetScrollContainer: (container) =>
+      @detachScroll()
+      @scrollContainer = container
+      @initScrollContainer()
+      @attachScroll()
+
     ##
     # Extends parent to detach scroll container event
     #