Add pinned posts (#4217)

webapp/sass/layout/_headers.scss

@@ -7,26 +7,43 @@
     line-height: 56px;
     width: 100%;
 
-    .member-popover__trigger {
+    .member-popover__trigger,
+    .pinned-posts-button {
+        display: inline-block;
+        min-width: 30px;
         cursor: pointer;
-        min-width: 60px;
-        padding-right: 10px;
-        text-align: right;
+        margin-left: 10px;
+        text-align: center;
         white-space: nowrap;
 
         .fa {
             font-size: 16px;
+        }
+    }
+
+    .member-popover__container,
+    .member-popover__trigger {
+        display: inline;
+    }
+
+    .member-popover__trigger {
+        .fa {
             margin-left: 4px;
         }
     }
 
+    .pinned-posts-button svg {
+        position: relative;
+        top: 2px;
+    }
+
     &.alt {
         margin: 0;
 
         th {
             font-weight: normal !important;
 
-            &.header-list__members {
+            &.header-list__right {
                 padding-right: 4px;
             }
         }