Add a warning icon to confidential issues on list page and issue details

app/views/projects/issues/_issue.html.haml

@@ -11,6 +11,10 @@
         %li
           CLOSED
 
+      - if issue.confidential?
+        %li
+          = icon('lock')
+
       - if issue.assignee
         %li
           = link_to_member(@project, issue.assignee, name: false, title: "Assigned to :name")

app/views/projects/issues/show.html.haml

@@ -22,6 +22,8 @@
       = icon('angle-double-left')
 
     .issue-meta
+      - if @issue.confidential
+        = icon('lock')
       %strong.identifier
         Issue ##{@issue.iid}
       %span.creator