Update screenshots

Fixes #7

CloudronManifest.json

@@ -20,10 +20,10 @@
   },
   "tags": [ "blog", "cms", "weblog" ],
   "mediaLinks": [
-    "https://wordpress.org/about/shots/1.5/front-page.png",
-    "https://wordpress.org/about/shots/1.5/front-2.png",
-    "https://wordpress.org/about/shots/1.5/front-5.png",
-    "https://wordpress.org/about/shots/1.5/front-3.png"
+    "https://codex.wordpress.org/File:twenty-seventeen-top.png",
+    "https://codex.wordpress.org/File:v47_editor-shortcuts-1.png",
+    "https://i1.wp.com/wordpress.org/news/files/2016/12/4.7-%E2%80%94-Nav.jpg?w=760&ssl=1",
+    "https://i2.wp.com/wordpress.org/news/files/2016/12/4.7-%E2%80%94-Language.jpg?w=760&ssl=1"
   ],
   "changelog": "file://CHANGELOG",
   "postInstallMessage": "file://POSTINSTALL.md",