fix(articles): Article edit/delete validation

Adds a custom field named `isCurrentUserOwner` to the Article document before
it's returned to the client. This field is used to determine if the current
User should is the "owner", and should see the edit/delete controls on the
client-side when viewing a single article. This custom (ad-hoc) field is NOT
persisted to the database; it's merely attached to the document.

Added server-side route tests for verifying the ad-hoc
"isCurrentUserOwner" field is properly set on the a single Article document.

Fixes #1146

modules/articles/server/controllers/articles.server.controller.js

@@ -30,7 +30,14 @@ exports.create = function (req, res) {
  * Show the current article
  */
 exports.read = function (req, res) {
-  res.json(req.article);
+  // convert mongoose document to JSON
+  var article = req.article ? req.article.toJSON() : {};
+
+  // Add a custom field to the Article, for determining if the current User is the "owner".
+  // NOTE: This field is NOT persisted to the database, since it doesn't exist in the Article model.
+  article.isCurrentUserOwner = req.user && article.user && article.user._id.toString() === req.user._id.toString() ? true : false;
+
+  res.json(article);
 };
 
 /**