for students, only display endorse icon if endorsed

lms/static/coffee/src/discussion/views/discussion_content_view.coffee

@@ -4,8 +4,12 @@ if Backbone?
     attrRenderer:
       endorsed: (endorsed) ->
         if endorsed
-          @$(".action-endorse").addClass("is-endorsed")
+          @$(".action-endorse").show().addClass("is-endorsed")
         else
+          if not @model.get('ability').can_endorse
+            @$(".action-endorse").hide()
+          else
+            @$(".action-endorse").show()
           @$(".action-endorse").removeClass("is-endorsed")
 
       closed: (closed) ->
@@ -47,8 +51,14 @@ if Backbone?
         enable: -> @$(".action-delete").closest("li").show()
         disable: -> @$(".action-delete").closest("li").hide()
       can_endorse:
-        enable: -> @$(".action-endorse").css("cursor", "auto")
-        disable: -> @$(".action-endorse").css("cursor", "default")
+        enable: ->
+          @$(".action-endorse").show().css("cursor", "auto")
+        disable: ->
+          @$(".action-endorse").css("cursor", "default")
+          if not @model.get('endorsed')
+            @$(".action-endorse").hide()
+          else
+            @$(".action-endorse").show()
       can_openclose:
         enable: -> @$(".action-openclose").closest("li").show()
         disable: -> @$(".action-openclose").closest("li").hide()

lms/templates/discussion/_underscore_templates.html

@@ -92,7 +92,7 @@
 <script type="text/template" id="thread-response-show-template">
     <header class="response-local">
         <a href="javascript:void(0)" class="vote-btn" data-tooltip="vote"><span class="plus-icon"></span><span class="votes-count-number">${"<%- votes['up_count'] %>"}</span></a>
-        <a href="javascript:void(0)" class="endorse-btn${'<% if (endorsed) { %> is-endorsed<% } %>'} action-endorse" style="cursor: default" data-tooltip="endorse"><span class="check-icon" style="pointer-events: none; "></span></a>
+        <a href="javascript:void(0)" class="endorse-btn${'<% if (endorsed) { %> is-endorsed<% } %>'} action-endorse" style="cursor: default; display: none;" data-tooltip="endorse"><span class="check-icon" style="pointer-events: none; "></span></a>
         <a href="${'<%- user_url %>'}" class="posted-by">${"<%- username %>"}</a>
         <p class="posted-details" title="${'<%- created_at %>'}">${'<%- created_at %>'}</p>
     </header>