Revert "Remove unused angular-feature-flags"

This patch failed to remove all vestiges of feature flags from
workPackagesTable directive.

This reverts commit c65d8ac4e8.

frontend/app/openproject-app.js

@@ -53,6 +53,7 @@ require('angular-ui-router');
 
 require('angular-ui-date');
 require('angular-truncate');
+require('angular-feature-flags');
 
 require('angular-busy/dist/angular-busy');
 require('angular-busy/dist/angular-busy.css');
@@ -180,6 +181,7 @@ var openprojectApp = angular.module('openproject', [
   'ngAria',
   'ngSanitize',
   'truncate',
+  'feature-flags',
   'openproject.layout',
   'cgBusy',
   'openproject.api',
@@ -224,15 +226,17 @@ openprojectApp
     '$http',
     '$rootScope',
     '$window',
+    'featureFlags',
     'TimezoneService',
     'KeyboardShortcutService',
-    function($http, $rootScope, $window, TimezoneService, KeyboardShortcutService) {
+    function($http, $rootScope, $window, flags, TimezoneService, KeyboardShortcutService) {
       $http.defaults.headers.common.Accept = 'application/json';
 
       $rootScope.showNavigation =
         $window.sessionStorage.getItem('openproject:navigation-toggle') !==
         'collapsed';
 
+      flags.set($http.get('/javascripts/feature-flags.json'));
       TimezoneService.setupLocale();
       KeyboardShortcutService.activate();
 

frontend/app/work_packages/directives/index.js

@@ -91,6 +91,7 @@ angular.module('openproject.workPackages.directives')
     'WorkPackagesTableService',
     '$window',
     '$timeout',
+    'featureFlags',
     'PathHelper',
     require('./work-packages-table-directive')
   ]);

frontend/webpack.config.js

@@ -118,6 +118,7 @@ module.exports = {
 
       'angular-ui-date': 'angular-ui-date/src/date',
       'angular-truncate': 'angular-truncate/src/truncate',
+      'angular-feature-flags': 'angular-feature-flags/dist/featureFlags.js',
       'angular-context-menu': 'angular-context-menu/dist/angular-context-menu.js',
       'mousetrap': 'mousetrap/mousetrap.js',
       'hyperagent': 'hyperagent/dist/hyperagent',

public/javascripts/feature-flags.json

@@ -0,0 +1,8 @@
+[
+    {
+        "key":        "detailsView",
+        "active":     true,
+        "name":       "Details View",
+        "description": "Displays details for individual work packages."
+    }
+]