CombinedSearch: Fix sort filter menus.

The js that controls the showing/hiding of the menus expect each dropdown
element to be the only instance amongst its siblings.  In other words, each
dropdown button and list must be wrapped in a container element for it to work
correctly.

Additionally, this moves the filter menus to the right side of the header for
better visibility.

r2/r2/public/static/css/search.less

@@ -188,6 +188,10 @@
     }
 
     .search-header-menus {
+      float: right;
+    }
+
+    .search-menu {
       .search-font-size(@search-font-base);
       display: inline-block;
       margin-left: @margin-large * 1px;

r2/r2/templates/searchlisting.html

@@ -35,7 +35,7 @@
         %if thing.nav_menus:
           <div class="search-header-menus">
             %for menu in thing.nav_menus:
-              ${menu}
+              <div class="search-menu">${menu}</div>
             %endfor
           </div>
         %endif