[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_rsa.php

@@ -75,6 +75,7 @@ class Activitypub_rsa extends Managed_DataObject
             if ($profile->isLocal()) {
                 self::generate_keys($this->private_key, $this->public_key);
                 $this->store_keys();
+                $apRSA->private_key = $this->private_key;
             } else {
                 throw new Exception('This is a remote Profile, there is no Private Key for this Profile.');
             }
@@ -100,6 +101,7 @@ class Activitypub_rsa extends Managed_DataObject
             if ($profile->isLocal()) {
                 self::generate_keys($this->private_key, $this->public_key);
                 $this->store_keys();
+                $apRSA->public_key = $this->public_key;
             } else {
                 // This should never happen, but try to recover!
                 if ($fetch) {