updated pinning icons and removed images

lms/static/sass/_discussion.scss

@@ -2645,7 +2645,7 @@ body.discussion {
   width: 10px; 
   height: 14px;
   padding-right: 3px;
-  background: transparent url('../images/unpinned.png') no-repeat 0 0; 
+  color: $gray-l2;
 }
 
 .pinned .icon {
@@ -2655,7 +2655,7 @@ body.discussion {
   width: 10px; 
   height: 14px; 
   padding-right: 3px;
-  background: transparent url('../images/pinned.png') no-repeat 0 0; 
+  color: $pink;
 }
 
 .pinned span {

lms/templates/discussion/_underscore_templates.html

@@ -53,12 +53,12 @@
         
       % if course and has_permission(user, 'openclose_thread', course.id):
       <div class="admin-pin discussion-pin notpinned" data-role="thread-pin" data-tooltip="pin this thread">                
-      <i class="icon"></i><span class="pin-label">Pin Thread</span></div> 
+      <i class="icon icon-pushpin"></i><span class="pin-label">Pin Thread</span></div> 
 
       %else:
       ${"<% if (pinned) { %>"}
       <div class="discussion-pin notpinned" data-role="thread-pin" data-tooltip="pin this thread">                
-      <i class="icon"></i><span class="pin-label">Pin Thread</span></div> 
+      <i class="icon icon-pushpin"></i><span class="pin-label">Pin Thread</span></div> 
       ${"<% }  %>"}  
       % endif