make fediverse module rely on REST API

I didn't want to do this unless we had to but Mastodon is introducing requirming
signed requests soon, so even if a user doesn't use bitbot as an instance, we'll
still need to be able to serve Actor (and key) over the REST API

modules/fediverse/__init__.py

@@ -1,3 +1,5 @@
+#--depends-on rest_api
+
 import urllib.parse
 from src import IRCBot, ModuleManager, utils
 from . import ap_actor, ap_security, ap_server, ap_utils