feat(collapse): Set display none when collapsed

This takes the element out of rendering to speed things up.

Author: chrisirhc

Diff for: src/collapse/collapse.js

@@ -49,10 +49,12 @@ angular.module('ui.bootstrap.collapse',['ui.bootstrap.transition'])
         if (initialAnimSkip) {
           initialAnimSkip = false;
           if ( !isCollapsed ) {
+            element.css('display', '');
             fixUpHeight(scope, element, 'auto');
             element.addClass('in');
           }
         } else {
+          element.css('display', '');
           doTransition({ height : element[0].scrollHeight + 'px' })
           .then(function() {
             // This check ensures that we don't accidentally update the height if the user has closed
@@ -72,9 +74,12 @@ angular.module('ui.bootstrap.collapse',['ui.bootstrap.transition'])
         if (initialAnimSkip) {
           initialAnimSkip = false;
           fixUpHeight(scope, element, 0);
+          element.css('display', 'none');
         } else {
           fixUpHeight(scope, element, element[0].scrollHeight + 'px');
-          doTransition({'height':'0'});
+          doTransition({'height':'0'}).then(function () {
+            element.css('display', 'none');
+          });
         }
       };
     }