bug #746 Including alerts.js and changing loading order (ptrm04, Peter)

This PR was merged into the master branch.

Discussion
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Including alerts.js and changing loading order

Alerts currently can't be dismissed in the symfony-demo app.
Also, updating the loading order to a correct one: https://github.com/twbs/bootstrap-sass#javascript

Commits
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5375d40 Adding .fade and .in to use animation when closing
b0ac79c Yarn'd for prod
c39d745 Yarn'd after including alert.js
10a7ba8 Fixing a typo
364c6b0 Including alerts.js and changing loading order

assets/js/app.js

@@ -1,8 +1,9 @@
 // loads the Bootstrap jQuery plugins
+import 'bootstrap-sass/assets/javascripts/bootstrap/transition.js';
+import 'bootstrap-sass/assets/javascripts/bootstrap/alert.js';
 import 'bootstrap-sass/assets/javascripts/bootstrap/collapse.js';
 import 'bootstrap-sass/assets/javascripts/bootstrap/dropdown.js';
 import 'bootstrap-sass/assets/javascripts/bootstrap/modal.js';
-import 'bootstrap-sass/assets/javascripts/bootstrap/transition.js';
 
 // loads the code syntax highlighting library
 import './highlight.js';