[ActivityPub] Ensuring federation with other software

ActivityPubPlugin:
- Prevent sending a Delete for an Announce

Activitypub_announce:
- Update announce_to_array to add id, to and cc information to the retrieved object

Activitypub_follow:
- Add id to the arguments of follow_to_array, useful for Accept-Follow activities

Activitypub_notice:
- Fix notice validation, url isn't a MUST

Activitypub_inbox_handler:
- Make handle_follow use the received activity id for the later Accept-Follow

Activitypub_postman:
- Fix call to the updated announce_to_array
- Fix successive unnecessary calls to ActivityPubPlugin::actor_uri()

plugins/ActivityPub/ActivityPubPlugin.php

@@ -747,10 +747,12 @@ class ActivityPubPlugin extends Plugin
             return true;
         }
 
-        // The deleting user must have permission to do so, but
-        // it still doesn't own the notitce, so we just need to
-        // handle things locally
-        if (!$notice->isLocal()) {
+        // We handle things locally either because:
+        // 1. the deleting user has special permissions to do so,
+        //    but still doesn't own the notice
+        // 2. the notice is an announce, and there's no undo-share
+        //    logic in GS's AP implementation
+        if (!$notice->isLocal() || $notice->isRepeat()) {
             return true;
         }