mod_rest: Fix nested message stanzas in XEP-0297 containers It's all a bit awkward because it doesn't normally use the whole schema directly, but rather checks which stanza type is used and picks out that property as a schema. Which also prevents references from working.

This module blocks configured queries that change server state.

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

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