bug #672 Fixed the responsive navigation menu (javiereguiluz)

This PR was merged into the master branch.

Discussion
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Fixed the responsive navigation menu

This fixes #670. The responsive menu now it works as expected:

![navbar](https://user-images.githubusercontent.com/73419/31537884-fac46ac0-b003-11e7-94d1-6fba6dc1ace7.gif)

The only important change is this one:

```diff
// assets/js/app.js
+import 'bootstrap-sass/assets/javascripts/bootstrap/collapse.js';
```

The other changes were introduced by Webpack automatically.

Commits
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18d8ec0 Fixed the responsive navigation menu

Author: javiereguiluz

assets/js/app.js

@@ -1,4 +1,5 @@
 // loads the Bootstrap jQuery plugins
+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';

public/build/css/app.css

@@ -1 +1,4 @@
-webpackJsonp([6],{nxx7:function(n,a,l){(function(n){n(function(){var a=n("#username"),l=n("#password");a.val()||l.val()||(a.val("jane_admin"),l.val("kitten"))})}).call(a,l("7t+N"))}},["nxx7"]);
+webpackJsonp([6],{nxx7:/*!****************************!*\
+  !*** ./assets/js/login.js ***!
+  \****************************/
+function(n,a,l){(function(n){n(function(){var a=n("#username"),l=n("#password");a.val()||l.val()||(a.val("jane_admin"),l.val("kitten"))})}).call(a,l(/*! jquery */"7t+N"))}},["nxx7"]);

public/build/js/admin.js

@@ -25,4 +25,4 @@
   "build/js/login.js": "/build/js/login.js",
   "build/js/search.js": "/build/js/search.js",
   "build/manifest.js": "/build/manifest.js"
-}
+}