Move more forum nav rendering logic to front end

The cohort selector is rendered only for a privileged user in a cohorted
course, and that logic is now in an Underscore template instead of Mako.

common/static/coffee/spec/discussion/view/discussion_thread_list_view_spec.coffee

@@ -75,6 +75,7 @@ describe "DiscussionThreadListView", ->
                             <option value="flagged">Flagged</option>
                         </select>
                     </label>
+                    <% if (isCohorted && isPrivilegedUser) { %>
                     <label class="forum-nav-filter-cohort">
                         <span class="sr">Cohort:</span>
                         <select class="forum-nav-filter-cohort-control">
@@ -83,6 +84,7 @@ describe "DiscussionThreadListView", ->
                             <option value="2">Cohort2</option>
                         </select>
                     </label>
+                    <% } %>
                     <label class="forum-nav-sort">
                         <select class="forum-nav-sort-control">
                             <option value="date">by recent activity</option>
@@ -123,7 +125,11 @@ describe "DiscussionThreadListView", ->
         spyOn($, "ajax")
 
         @discussion = new Discussion([])
-        @view = new DiscussionThreadListView({collection: @discussion, el: $("#fixture-element")})
+        @view = new DiscussionThreadListView(
+          collection: @discussion,
+          el: $("#fixture-element"),
+          courseSettings: new DiscussionCourseSettings({is_cohorted: true})
+        )
         @view.render()
 
     setupAjax = (callback) ->
@@ -141,7 +147,8 @@ describe "DiscussionThreadListView", ->
     makeView = (discussion) ->
       return new DiscussionThreadListView(
           el: $("#fixture-element"),
-          collection: discussion
+          collection: discussion,
+          courseSettings: new DiscussionCourseSettings({is_cohorted: true})
       )
 
     expectFilter = (filterVal) ->
@@ -164,7 +171,12 @@ describe "DiscussionThreadListView", ->
         )
 
     describe "cohort selector", ->
-        it "should filter correctly", ->
+        it "should not be visible to students", ->
+            expect(@view.$(".forum-nav-filter-cohort-control:visible")).not.toExist()
+
+        it "should allow moderators to select visibility", ->
+            DiscussionSpecHelper.makeModerator()
+            @view.render()
             expectedGroupId = null
             setupAjax((params) => expect(params.data.group_id).toEqual(expectedGroupId))
             _.each(
@@ -498,6 +510,8 @@ describe "DiscussionThreadListView", ->
           expect($(".forum-nav-browse-current").text()).toEqual("Posts I'm Following")
 
         it "should show/hide the cohort selector", ->
+          DiscussionSpecHelper.makeModerator()
+          @view.render()
           setupAjax()
           _.each(
             [

common/static/coffee/src/discussion/discussion_router.coffee

@@ -8,7 +8,11 @@ if Backbone?
         @discussion = options['discussion']
         @course_settings = options['course_settings']
 
-        @nav = new DiscussionThreadListView(collection: @discussion, el: $(".forum-nav"))
+        @nav = new DiscussionThreadListView(
+            collection: @discussion,
+            el: $(".forum-nav"),
+            courseSettings: @course_settings
+        )
         @nav.on "thread:selected", @navigateToThread
         @nav.on "thread:removed", @navigateToAllThreads
         @nav.on "threads:rendered", @setActiveThread

common/static/coffee/src/discussion/views/discussion_thread_list_view.coffee

@@ -13,7 +13,8 @@ if Backbone?
       "change .forum-nav-filter-main-control": "chooseFilter"
       "change .forum-nav-filter-cohort-control": "chooseCohort"
 
-    initialize: ->
+    initialize: (options) ->
+      @courseSettings = options.courseSettings
       @displayedCollection = new Discussion(@collection.models, pages: @collection.pages)
       @collection.on "change", @reloadDisplayedCollection
       @discussionIds=""
@@ -121,7 +122,12 @@ if Backbone?
 
     render: ->
       @timer = 0
-      @$el.html(@template())
+      @$el.html(
+        @template({
+          isCohorted: @courseSettings.get("is_cohorted"),
+          isPrivilegedUser: DiscussionUtil.isPrivilegedUser()
+        })
+      )
       @$(".forum-nav-sort-control").val(@collection.sort_preference)
 
       $(window).bind "load", @updateSidebar

lms/templates/discussion/_thread_list_template.html

@@ -37,10 +37,7 @@
                         <option value="flagged">${_("Flagged")}</option>
                     %endif
                 </select>
-            </label>\
-            %if is_course_cohorted and is_moderator:
-## Lack of indentation is intentional to avoid whitespace between this and siblings
-<label class="forum-nav-filter-cohort">
+            </label>${"<% if (isCohorted && isPrivilegedUser) { %>"}<label class="forum-nav-filter-cohort">
                 ## Translators: This labels a cohort menu in forum navigation
                 <span class="sr">${_("Cohort:")}</span>
                 <select class="forum-nav-filter-cohort-control">
@@ -49,10 +46,7 @@
                             <option value="${c['id']}">${c['name']}</option>
                         %endfor
                 </select>
-            </label>\
-            %endif
-## Lack of indentation is intentional to avoid whitespace between this and siblings
-<label class="forum-nav-sort">
+            </label>${"<% } %>"}<label class="forum-nav-sort">
                 ## Translators: This labels a sort menu in forum navigation
                 <span class="sr">${_("Sort:")}</span>
                 <select class="forum-nav-sort-control">