spotlight: Fade before first item is displayed.

This is intended to reduce the perceptual flash when promos load in.

r2/r2/public/static/css/reddit.less

@@ -957,6 +957,15 @@ a.author { margin-right: 0.5em; }
     overflow: hidden; 
     position: relative;
     min-height: 50px; 
+
+    &.loading {
+        height: 62px;
+        opacity: .5;
+
+        & .help, & .throbber {
+            display: none;
+        }
+    }
 }
 
 .organic-listing .link {

r2/r2/public/static/js/spotlight.js

@@ -136,6 +136,7 @@ r.spotlight._advance = function(dir) {
         }
 
         $nextprev.removeClass('working')
+        listing.removeClass('loading')
 
         // size the rank element so that spotlight box
         // items line up with the main page listing

r2/r2/templates/spotlightlisting.html

@@ -28,7 +28,7 @@
    from r2.lib.wrapped import Templated
 %>
 
-<div id="siteTable_organic" class="organic-listing">
+<div id="siteTable_organic" class="organic-listing loading">
   %if thing.things:
     %for link in thing.things:
       ${unsafe(link.render(display=False))}