mod_storage_xmlarchive: Ensure list index files are removed using os.remove() on the list files leaves the new index files behind since util.datamanager does not know they are removed. Thanks Link Mauve

This module blocks configured queries that change server state.

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

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