feat(alert): pass $event to close()

Add ability to hook into `$event` in close callback

Closes #3828
Fixes #3827

Author: Avi Cherry

Diff for: template/alert/alert.html

@@ -1,5 +1,5 @@
 <div class="alert" ng-class="['alert-' + (type || 'warning'), closeable ? 'alert-dismissible' : null]" role="alert">
-    <button ng-show="closeable" type="button" class="close" ng-click="close()">
+    <button ng-show="closeable" type="button" class="close" ng-click="close($event)">
         <span aria-hidden="true">&times;</span>
         <span class="sr-only">Close</span>
     </button>