Make system note different from regular comments

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/pages/notes.scss

@@ -14,6 +14,19 @@ ul.notes {
   margin: 0px;
   padding: 0px;
 
+  .system-note {
+    font-size: 14px;
+    padding-top: 10px;
+    padding-bottom: 10px;
+    background: #f8fafc;
+
+    .timeline-icon {
+      .avatar {
+        visibility: hidden;
+      }
+    }
+  }
+
   .discussion-header,
   .note-header {
     @extend .cgray;

app/views/projects/notes/_discussion.html.haml

 - note = discussion_notes.first
-.timeline-entry
+.timeline-entry.prepend-top-default
   .timeline-entry-inner
     .timeline-icon
       = link_to user_path(note.author) do