Use webpack to deliver underscore (and use newest version)

app/assets/javascripts/application.js

@@ -23,5 +23,4 @@
 //= require ace/ace
 //= require ace/ext-language_tools
 //= require jquery-ui.min
-//= require underscore.min
 //= require_tree .

app/javascript/packs/application.js

@@ -12,6 +12,8 @@ import 'jquery'
 import 'bootstrap/dist/js/bootstrap.bundle.min';
 import 'chosen-js/chosen.jquery';
 import 'jstree';
+import 'underscore';
+window._ = _; // Publish underscore's `_` in global namespace
 
 // CSS
 import 'chosen-js/chosen.css';