Implement "translations" AMD

This module is used to get translated messages via JSON
request in a synchronous manner. To ensure translatability
i18n messages should be initialized before any other JS code
interacted with user is run.

Fixes: https://pagure.io/freeipa/issue/7559
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Petr Vobornik <pvoborni@redhat.com>

install/ui/src/freeipa/config.js

@@ -43,6 +43,11 @@ define([
          */
         url: '/ipa/ui/',
 
+        /**
+         * i18n messages url
+         */
+        i18n_messages_url: '/ipa/i18n_messages',
+
         /**
          * RPC url
          */

install/ui/src/freeipa/translations.js

@@ -0,0 +1,72 @@
+//
+// Copyright (C) 2018  FreeIPA Contributors see COPYING for license
+//
+
+define([
+    './jquery',
+    './config',
+    './_base/i18n'
+   ],
+   function( $, config, i18n) {
+
+ /**
+  *
+  * Retrieve translations from server
+  *
+  * @class translations
+  * @singleton
+  *
+  */
+
+var translations = {};
+
+var retrieve  = function() {
+
+    var result = false;
+
+    var jsondata = {
+        method: "i18n_messages",
+        params: [ [], { "version": window.ipa_loader.api_version } ]
+    };
+
+    var json_url = config.i18n_messages_url;
+
+    // test case: tests dir with crafted data stored in the local json file
+    if (window.location.protocol === 'file:') {
+        json_url = "data/" + jsondata.method + '.json';
+    }
+
+    var request = {
+        method: 'POST',
+        url: json_url,
+        data: JSON.stringify(jsondata),
+        dataType: "json",
+        contentType: 'application/json',
+        async: false,
+        processData: false,
+        success: success_handler,
+        error: error_handler
+    };
+
+    function error_handler(xhr, text_status, error_thrown) {
+        result = false;
+    }
+
+    function success_handler(data, text_status, xhr) {
+        if (!data.error) {
+            i18n.source = data.result.texts;
+            result = true;
+        }
+    }
+
+    $.ajax(request);
+    return result;
+};
+
+if (!retrieve()) {
+    throw new Error('Couldn\'t receive translations');
+}
+
+translations.update = retrieve;
+return translations;
+});