[ActivityPub] Caching of Following/Followers interactions and collections

Follow interaction:
- Fixed mini-bug where the subscriber profile was being used as the subscribed
- Updated cache subscription-related values in both instances
- Tested and working with local GS instances

Unfollow interaction:
- Updated cache subscription-related values in both instances
- Tested and working with local GS instances

Followers/Following collections:
- Now returning ActivityPub profiles only
- Stored collections in cache

Misc:
- Fix bug concerning the retrieval of public/private-key after in-function generation

plugins/ActivityPub/classes/Activitypub_follow.php

@@ -78,6 +78,7 @@ class Activitypub_follow extends Managed_DataObject
 
         if (!Subscription::exists($actor_profile, $object_profile)) {
             Subscription::start($actor_profile, $object_profile);
+            Activitypub_profile::subscribeCacheUpdate($actor_profile, $object_profile);
             common_debug('ActivityPubPlugin: Accepted Follow request from '.ActivityPubPlugin::actor_uri($actor_profile).' to '.$object);
         } else {
             common_debug('ActivityPubPlugin: Received a repeated Follow request from '.ActivityPubPlugin::actor_uri($actor_profile).' to '.$object);
@@ -85,7 +86,7 @@ class Activitypub_follow extends Managed_DataObject
 
         // Notify remote instance that we have accepted their request
         common_debug('ActivityPubPlugin: Notifying remote instance that we have accepted their Follow request request from '.ActivityPubPlugin::actor_uri($actor_profile).' to '.$object);
-        $postman = new Activitypub_postman($actor_profile, [$actor_aprofile]);
+        $postman = new Activitypub_postman($object_profile, [$actor_aprofile]);
         $postman->accept_follow();
     }
 }