Mark notification as read without visiting discussion (#1874)

less/forum/NotificationList.less

@@ -87,6 +87,10 @@
   &:hover {
     text-decoration: none;
     background: @control-bg;
+    
+    .Notification-action {
+      display: block;
+    }
   }
   .Avatar {
     .Avatar--size(24px);
@@ -98,6 +102,27 @@
     font-weight: bold;
     text-transform: uppercase;
   }
+
+  .Notification-action {
+    float: right;
+    display: none;
+    margin-top: -7px;
+    margin-right: -10px;
+    line-height: inherit;
+    padding: 5px 0;
+
+    & when (@config-colored-header = true) {
+      .Button--color(@control-color, @control-bg);
+
+      &:hover {
+        color: @link-color;
+      }
+    }
+
+    .icon {
+      font-size: 12px;
+    }
+  }
 }
 .Notification-icon {
   float: left;