Responsive display utilities (#20934)

* Explore responsive display utils, but with a twist: lowest breakpoint has no breakpoint modifier in the class name
* make floats use the same format, add float-none mixin

js/dist/alert.js

@@ -4,7 +4,7 @@ function _classCallCheck(instance, Constructor) { if (!(instance instanceof Cons
 
 /**
  * --------------------------------------------------------------------------
- * Bootstrap (v4.0.0-alpha.5): alert.js
+ * Bootstrap (v4.0.0-alpha.4): alert.js
  * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
  * --------------------------------------------------------------------------
  */
@@ -18,7 +18,7 @@ var Alert = function ($) {
    */
 
   var NAME = 'alert';
-  var VERSION = '4.0.0-alpha.5';
+  var VERSION = '4.0.0-alpha.4';
   var DATA_KEY = 'bs.alert';
   var EVENT_KEY = '.' + DATA_KEY;
   var DATA_API_KEY = '.data-api';
@@ -38,7 +38,7 @@ var Alert = function ($) {
   var ClassName = {
     ALERT: 'alert',
     FADE: 'fade',
-    ACTIVE: 'active'
+    IN: 'in'
   };
 
   /**
@@ -101,18 +101,14 @@ var Alert = function ($) {
     };
 
     Alert.prototype._removeElement = function _removeElement(element) {
-      var _this = this;
-
-      $(element).removeClass(ClassName.ACTIVE);
+      $(element).removeClass(ClassName.IN);
 
       if (!Util.supportsTransitionEnd() || !$(element).hasClass(ClassName.FADE)) {
         this._destroyElement(element);
         return;
       }
 
-      $(element).one(Util.TRANSITION_END, function (event) {
-        return _this._destroyElement(element, event);
-      }).emulateTransitionEnd(TRANSITION_DURATION);
+      $(element).one(Util.TRANSITION_END, $.proxy(this._destroyElement, this, element)).emulateTransitionEnd(TRANSITION_DURATION);
     };
 
     Alert.prototype._destroyElement = function _destroyElement(element) {