muc_notifications: notify non-present members of new messages This module, in the event of a new message in a Group Chat, will generate a notification for each of those members not present at that time in the Group Chat

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```