Add basic Matrix puppeting support

May contain bugs.
EDUs from /sync are not yet handled.

example-config.yaml

@@ -81,6 +81,10 @@ bridge:
     # Default is 3 days = 259200 seconds
     sync_max_chat_age: 259200
 
+    # Whether or not to sync with custom puppets to receive EDUs that
+    # are not normally sent to appservices.
+    sync_with_custom_puppets: true
+
     # The prefix for commands. Only required in non-management rooms.
     command_prefix: "!wa"