mod_http_muc_log: Correctly handle changed or retracted reactions Since per XEP-0444 each reaction should overwrite all previous reactions on a particular message from a particular occupant. Previously repeated reactions would be counted again and retractions were not handled.

This module blocks configured queries that change server state.

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

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