mod_groups_internal: allow force-emitting group member addition events This is useful when a new plugin was loaded which handles that event to add some value. Then the command can be called (**not** from the plugin but from an upcoming admin shell module) to synchronise things.

This module discards typing notifications sent to a bare host JID,
preventing error replies to be sent. These errors are harmless but can
be annoying sometimes if your client shows them prominently.