fix cors problems with newsfeed articles (#2940)

solves #2840 as far as possible. There could still be errors on the
embedded iframe when the owner of the site has set `X-Frame-Options` or
`Access-Control-Allow-Origin` headers (as already mentioned in the
docs).

modules/default/newsfeed/newsfeedfetcher.js

@@ -18,9 +18,10 @@ const stream = require("stream");
  * @param {number} reloadInterval Reload interval in milliseconds.
  * @param {string} encoding Encoding of the feed.
  * @param {boolean} logFeedWarnings If true log warnings when there is an error parsing a news article.
+ * @param {boolean} useCorsProxy If true cors proxy is used for article url's.
  * @class
  */
-const NewsfeedFetcher = function (url, reloadInterval, encoding, logFeedWarnings) {
+const NewsfeedFetcher = function (url, reloadInterval, encoding, logFeedWarnings, useCorsProxy) {
 	let reloadTimer = null;
 	let items = [];
 
@@ -57,7 +58,8 @@ const NewsfeedFetcher = function (url, reloadInterval, encoding, logFeedWarnings
 					title: title,
 					description: description,
 					pubdate: pubdate,
-					url: url
+					url: url,
+					useCorsProxy: useCorsProxy
 				});
 			} else if (logFeedWarnings) {
 				Log.warn("Can't parse feed item:");