Listen to row hovers on table instead of body

This won't work for tables dynamically added to the page, but at the
moment we don't have any of those.

From the jquery docs:

  Attaching many delegated event handlers near the top of the document
  tree can degrade performance. Each time the event occurs, jQuery must
  compare all selectors of all attached events of that type to every
  element in the path from the event target up to the top of the
  document.  For best performance, attach delegated events at a document
  location as close as possible to the target elements. Avoid excessive
  use of document or document.body for delegated events on large
  documents.

backend/app/assets/javascripts/spree/backend/admin.js

@@ -24,13 +24,13 @@ jQuery(function($) {
   });
 
   // Highlight hovered table column
-  $('body').on("mouseenter", 'td.actions a, td.actions button', function(){
+  $('table').on("mouseenter", 'td.actions a, td.actions button', function(){
     var tr = $(this).closest('tr');
     var klass = 'highlight action-' + $(this).data('action')
     tr.addClass(klass)
     tr.prev().addClass('before-' + klass);
   });
-  $('body').on("mouseleave", 'td.actions a, td.actions button', function(){
+  $('table').on("mouseleave", 'td.actions a, td.actions button', function(){
     var tr = $(this).closest('tr');
     var klass = 'highlight action-' + $(this).data('action')
     tr.removeClass(klass)